Annex A : Module ISO_varying_string
This part of ISO/IEC 1539 defines the interface and semantics for a module that provides facilities for the manipulation of character strings of arbitrary and dynamically variable length. Annex A includes a possible implementation, in Fortran 90, of a module that conforms to this part of ISO/IEC 1539. It should be noted, however, that this is purely for purposes of demonstrating the feasibility and portability of this standard. The actual code shown in this annex is not intended in any way to prescribe the method of implementation, nor is there any implication that this is in any way an optimal portable implementation. The module is merely a fairly straightforward demonstration that a portable implementation is possible.
This part of ISO/IEC 1539 prescribes the name of a Fortran module, the name of a derived data type to be used to represent varying-length strings, the interfaces for the procedures and operators to be provided to manipulate objects of this type, and the semantics that are required for each of the entities made accessible by this module.
This part of ISO/IEC 1539 does not prescribe the details of any implementation. Neither the method used to represent the data entities of the defined type nor the algorithms used to implement the procedures or operators whose interfaces are defined by this part of ISO/IEC 1539 are prescribed. A conformant implementation may use any representation and any algorithms, subject only to the requirement that the publicly accessible names and interfaces conform to this part of ISO/IEC 1539, and that the semantics are as required by this part of ISO/IEC 1539 and those of ISO/IEC 1539 : 1991.
It should be noted that a processor is not required to implement this part of ISO/IEC 1539 in order to be a standard conforming Fortran processor, but if a processor implements facilities for manipulating varying length character strings, it is recommended that this be done in a manner that is conformant with this part of ISO/IEC 1539.
A processor conforming to this part of ISO/IEC 1539 may extend the facilities provided for the manipulation of varying length character strings as long as such extensions do not conflict with this part of ISO/IEC 1539 or with ISO/IEC 1539 : 1991.
A module, written in standard conforming Fortran, is included in Annex A. This module illustrates one way in which the facilities described in this part of ISO/IEC 1539 could be provided. This module is both conformant with the requirements of this part of ISO/IEC 1539 and, because it is written in standard conforming Fortran, it provides a portable implementation of the required facilities. This module is included for information only and is not intended to constrain implementations in any way. This module is a demonstration that at least one implementation, in standard conforming and hence portable Fortran, is possible.
It should be noted that this part of ISO/IEC 1539 defines facilities for dynamically varying length strings of characters of default kind only. Throughout this part of ISO/IEC 1539 all references to intrinsic type CHARACTER should be read as meaning characters of default kind. Similar facilities could be defined for non-default kind characters by a separate, if similar, module for each such character kind.
This part of ISO/IEC 1539 has been designed, as far as is reasonable, to provide for varying length character strings the facilities that are available for intrinsic fixed length character strings. All the intrinsic operations and functions that apply to fixed length character strings have extended meanings defined by this part of ISO/IEC 1539 for varying length character strings. Also a small number of additional facilities are defined that are appropriate because of the essential differences between the intrinsic type and the varying length derived data type.
ISO/IEC 646 : 1991, Information technology - ISO 7-bit Coded character set for information interchange.
ISO/IEC 1539 : 1991, Information technology - Programming Languages - Fortran.
ISO_VARYING_STRING
Programs shall be able to access the facilities defined by this part of ISO/IEC 1539 by the inclusion of USE statements of the form
USE ISO_VARYING_STRING
VARYING_STRING
Entities of this type shall represent values that are strings of characters of default kind. These character strings may be of any non-negative length and this length may vary dynamically during the execution of a program. There shall be no arbitrary upper length limit other than that imposed by the size of the processor and the complexity of the programs it is able to process. The characters representing the value of the string have positions 1,2,...,N, where N is the length of the string. The internal structure of the type shall be PRIVATE to the module.
assignment =
concatenation //
comparisons ==, /=, <, <=, >=, >
shall be extended to accept any combination of scalar operands of type VARYING_STRING and type CHARACTER. Note that the equivalent comparison operator forms .EQ., .NE., .LT., .LE., .GE., and .GT. also have their meanings extended in this manner.
var = expr
shall be defined for scalars with the following type combinations:
Case(i): Where the variable is of type VARYING_STRING, the length of the variable becomes that of the expression.
Case(ii): Where the variable is of type CHARACTER, the rules of intrinsic assignment to a Fortran character variable apply. Namely, if the expression string is longer than the declared length of the character variable, only the left-most characters are assigned. If the character variable is longer than that of the string expression, it is padded on the right with blanks.
string_a // string_b
shall be defined for scalars with the following type combinations:
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is a new string whose characters are the same as those produced by concatenating the operand character strings in the order given.
string_a .OP. string_b
where .OP. represents any of the operators ==, /=, <, <=, >=, or > shall be defined for scalar operands with the following type combinations:
Note that the equivalent operator forms .EQ., .NE., .LT., .LE., .GE., and .GT. also have their meanings extended in this manner.
Result Attributes: scalar of type default LOGICAL.
Result Value: The result value is true if string_a stands in the indicated relation to string_b and is false otherwise. The collating sequence used for the inequality comparisons is that defined by the processor for characters of default kind. If string_a and string_b are of different lengths, the comparison is done as if the shorter string were padded on the right with blanks.
LEN(string)
shall be added.
Description: returns the length of a character string.
Argument: string is a scalar of type VARYING_STRING. The argument is unchanged by the procedure.
Result Attributes: scalar of type default INTEGER.
Result Value: The result value is the number of characters in string.
Description: converts a varying string value to default character.
Arguments:
string - is of type VARYING_STRING
length - is of type default INTEGER.
The arguments are scalars and are unchanged by the procedure.
Result Attributes: scalar of type default CHARACTER. If length is absent, the result has the same length as string. If length is present, the result has the length specified by the argument length.
Result Value:
Case(i): If length is absent, the result is a copy of the characters in the argument string.
Case(ii): If length is present, the result is a copy of the characters in the argument string that may have been truncated or padded. If string is longer than length, the result is truncated on the right. If string is shorter than length, the result is padded on the right with blanks. If length is less than one, the result is of zero length.
ICHAR(c)
shall be added.
Description: returns the position of a character in the processor defined collating
sequence.
Argument: c is a scalar of type VARYING_STRING and of length exactly one. The
argument is unchanged by the procedure.
Result Attributes: scalar of type default INTEGER.
Result Value: The result value is the position of the character c in the processor
defined collating sequence for default characters. That is, the result value is
ICHAR(CHAR(c)).
IACHAR(c)
shall be added.
Description: returns the position of a character in the collating sequence defined by
the International Standard ISO 646 : 1991.
Argument: c is a scalar of type VARYING_STRING and of length exactly one. The
argument is unchanged by the procedure.
Result Attributes: scalar of type default INTEGER.
Result Value: The result value is the position of the character c in the collating
sequence defined by the International Standard ISO 646 : 1991 for default characters.
If the character c is not defined in the standard set, the result is processor
dependent but is always equal to IACHAR(CHAR(c).
TRIM(string)
shall be added.
Description: removes trailing blanks from a string.
Argument: string is a scalar of type VARYING_STRING. The argument is unchanged
by the procedure.
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is the same as string except that any trailing blanks
have been deleted. If the argument string contains only blank characters or is of
zero length, the result is a zero-length string.
LEN_TRIM(string)
shall be added.
Description: returns the length of a string not counting any trailing blanks.
Argument: string is a scalar of type VARYING_STRING. The argument is unchanged
by the procedure.
Result Attributes: scalar of type default INTEGER.
Result Value: The result value is the position of the last non-blank character in
string. If the argument string contains only blank characters or is of zero length,
the result is zero.
ADJUSTL(string)
shall be added.
Description: adjusts to the left, removing any leading blanks and inserting trailing
blanks.
Argument: string is a scalar of type VARYING_STRING. The argument is unchanged
by the procedure.
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is the same as string except that any leading blanks
have been deleted and the same number of trailing blanks inserted.
ADJUSTR(string)
shall be added.
Description: adjusts to the right, removing any trailing blanks and inserting leading
blanks.
Argument: string is a scalar of type VARYING_STRING. The argument is unchanged
by the procedure.
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is the same as string except that any trailing blanks
have been deleted and the same number of leading blanks inserted.
REPEAT(string,ncopies)
shall be added.
Description: concatenates several copies of a string.
Arguments:
string - is a scalar of type VARYING_STRING,
ncopies - is a scalar of type default INTEGER.
The value of ncopies must not be negative. The arguments are unchanged by the
procedure.
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is the string produced by repeated concatenation of the
argument string, producing a string containing ncopies copies of string. If
ncopies is zero, the result is of zero length.
Lop(string_a,string_b
shall be added, where op stands for one of:
LT - less than
LE - less than or equal to
GE - greater than or equal to
GT - greater than
Description: compares the lexical ordering of two strings based on the ISO 646 : 1991
collating sequence.
Arguments: string_a and string_b are scalars of one of the type combinations:
Result Attributes: scalar of type default LOGICAL.
Result Value: The result value is true if string_a stands in the indicated relationship
to string_b, and is false otherwise. The collating sequence used to establish the
ordering of characters for these procedures is that of the International Standard ISO
646 : 1991. If string_a and string_b are of different lengths, the comparison is
done as if the shorter string were padded on the right with blanks. If either argument
contains a character c not defined by the standard, the result value is processor
dependent and based on the collating value for IACHAR(c. Zero length strings are
considered to be lexically equal.
INDEX(string,substring,back)
shall be added.
Description: returns an integer that is the starting position of a substring within a
string.
Arguments: string and substring are scalars of one of the type combinations:
The arguments are unchanged by the procedure.
Result Attributes: scalar of type default INTEGER.
Result value:
Case(i): If back is absent or is present with the value false, the result is the
minimum positive value of I such that,
EXTRACT(string,I,I+LEN(substring)-1)==substring, or zero if there is no such value.
Zero is returned if LEN(string)<LEN(substring), and one
is returned if LEN(substring)==0.
Case(ii): If back is present with the value true, the result is the
maximum value of I less than or equal to
LEN(string)-LEN(substring)+1 such that
EXTRACT(string,I,I+LEN(substring)-1)==substring, or zero if there is no such value.
Zero is returned if LEN(string)<LEN(substring), and
LEN(string)+1 is returned if LEN(substring)==0.
SCAN(string,set,back)
shall be added.
Description: scans a string for any one of the characters in a set of characters.
Arguments: string and set are scalars of one of the type combinations:
The arguments are unchanged by the procedure.
Result Attributes: scalar of type default INTEGER.
Result Value:
Case(i): If back is absent or is present with the value false and if string
contains at least one character that is in set, the value of the result
is the position of the left-most character of string that is in set.
Case(ii): If back is present with the value true and if string contains
at least one character that is in set, the value of the result
is the position of the right-most character of string that
is in set.
Case(iii): The value of the result is zero if no character of string is
in set or if the length of either string or set is zero.
VERIFY(string,set,back)
shall be added.
Description: verifies that a string contains only characters from a given set by
scanning for any character not in the set.
Arguments: string and set are scalars of one of the type combinations:
The arguments are unchanged by the procedure.
Result Attributes: scalar of type default INTEGER.
Result Value:
Case(i): If back is absent or is present with the value false and if string
contains at least one character that is not in set, the value of the
result is the position of the left-most character of string that is
not in set.
Case(ii): If back is present with the value true and if string contains
at least one character that is not in set, the value of the
result is the position of the right-most character of string
that is not in set.
Case(iii): The value of the result is zero if each character of string is
in set or if the length of string is zero.
The generic function reference of the form
The generic function reference of the form
The generic function reference of the form
The generic function reference of the form
The generic function reference of the form
The generic function reference of the form
The set of generic function references of the form
The generic function reference of the form
The generic function reference of the form
The generic function reference of the form
VAR_STR(char)
shall be provided.
Description: converts an intrinsic fixed-length character value into the equivalent varying-length string value.
Argument: char is a scalar of type default CHARACTER and may be of any length. The argument is unchanged by the procedure.
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is the same string of characters as the argument.
GET - input part or all of a record into a string
PUT - append a string to an output record
PUT_LINE - append a string to an output record and end the record
Description: reads characters from an external file into a string.
Arguments:
string - is of type VARYING_STRING,
maxlen - is of type default INTEGER and is OPTIONAL,
unit - is of type default INTEGER,
set - is either of type VARYING_STRING or of type CHARACTER,
separator - is of type VARYING_STRING and is OPTIONAL,
iostat - is of type default INTEGER and is OPTIONAL.
All arguments are scalar. The argument unit specifies the input unit to be used. It must be connected to a formatted file for sequential read access. If the argument unit is omitted, the default input unit is used. The arguments maxlen, unit, and set are unchanged by the procedure.
Action: The GET procedure causes characters from the connected file, starting with the next character in the current record if there is a current record or the first character of the next record if not, to be read and stored in the variable string. The end of record always terminates the input but input may be terminated before this. If maxlen is present, its value indicates the maximum number of characters that will be read. If maxlen is less than or equal to zero, no characters will be read and string will be set to zero length. If maxlen is absent, a maximum of HUGE(1) is used. If the argument set is provided, this specifies a set of characters the occurrence of any of which will terminate the input. This terminal character, although read from the input file, will not be included in the result string. The file position after the data transfer is complete, is after the last character that was read. If the argument separator is present, the actual character found which terminates the transfer is returned in separator. If the transfer is terminated other than by the occurrence of a character in set, a zero length string is returned in separator. If the transfer is terminated by the end of record being reached, the file is positioned after the record just read. If present, the argument iostat is used to return the status resulting from the data transfer. A zero value is returned if a valid read operation occurs and the end-of-record is not reached, a positive value if an error occurs, and a negative value if an end-of-file or end-of-record condition occurs. Note, the negative value returned for an end-of-file condition must be different from that returned for an end-of-record condition. If iostat is absent and an error or end-of-file condition occurs, the program execution is terminated.
CALL PUT(string,iostat)
CALL PUT(unit,string,iostat)
shall be provided.
Description: writes a string to an external file.
Arguments:
string - is either of type VARYING_STRING or type CHARACTER,
unit - is of type default INTEGER,
iostat - is of type default INTEGER and is OPTIONAL.
All arguments are scalar. The argument unit specifies the output unit to be used. It must be connected to a formatted file for sequential write access. If the argument unit is omitted, the default output unit is used. The arguments unit and string are unchanged by the procedure.
Action: The PUT procedure causes the characters of string to be appended to the current record, if there is a current record, or to the start of the next record if there is no current record. The last character transferred becomes the last character of the current record, which is the last record of the file. If present, the argument iostat is used to return the status resulting from the data transfer. A zero value is returned if a valid write operation occurs, and a positive value if an error occurs. If iostat is absent and anything other than a valid write operation occurs, the program execution is terminated.
CALL PUT_LINE(string,iostat)
CALL PUT_LINE(unit,string,iostat)
shall be provided.
Description: writes a string to an external file and ends the record.
Arguments:
string - is either of type VARYING_STRING or type CHARACTER
unit - is of type default INTEGER
iostat - is of type default INTEGER and is OPTIONAL.
All arguments are scalar. The argument unit specifies the output unit to be used. It must be connected to a formatted file for sequential write access. If the argument unit is omitted, the default output unit is used. The arguments unit and string are unchanged by the procedure.
Action: The PUT_LINE procedure causes the characters of string to be appended to the current record, if there is a current record, or to the start of the next record if there is no current record. Following completion of the data transfer, the file is positioned after the record just written, which becomes the previous and last record of the file. If present, the argument iostat is used to return the status resulting from the data transfer. A zero value is returned if a valid write operation occurs, and a positive value if an error occurs. If iostat is absent and anything other than a valid write operation occurs, the program execution is terminated.
INSERT - insert a substring into a string
REPLACE - replace a substring in a string
REMOVE - remove a section of a string
EXTRACT - extract a section from a string
SPLIT - split a string into two at the occurrence of a separator
INSERT(string,start,substring)
shall be provided.
Description: inserts a substring into a string at a specified position.
Arguments:
string - is either type VARYING_STRING or type default CHARACTER,
start - is type default INTEGER,
substring - is either type VARYING_STRING or type default CHARACTER.
All arguments are scalars. The arguments are unchanged by the procedure.
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is a copy of the characters of the argument string with the characters of substring inserted into the copy of string before the character at the character position start. If start is greater than LEN(string, the value LEN(string)+1) is used for start and substring is appended to the copy of string. If start is less than one, the value one is used for start and substring is inserted before the first character of the copy of string.
Description: replaces a subset of the characters in a string by a given substring. The subset may be specified either by position or by content.
Arguments:
string - is either of type VARYING_STRING or type default CHARACTER,
start - is of type default INTEGER,
finish - is of type default INTEGER,
substring - is either of type VARYING_STRING or type default CHARACTER,
target - is either of type VARYING_STRING or type default CHARACTER,
every - is of type default LOGICAL, and is OPTIONAL,
back - is of type default LOGICAL, and is OPTIONAL.
All arguments are scalar. The argument target must not be of zero length. In all cases the arguments are unchanged by the procedure.
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is a copy of the characters in string modified as per one of the cases below.
Case(i): For a reference of the form
REPLACE(string,start,substring)
the characters of the argument substring are inserted into the copy of string beginning with the character at the character position start. The characters in positions from
start to MIN(start+LEN(substring)-1,LEN(string)
are deleted. If start is greater than LEN(string), the value LEN(string)+1 is used for start and substring is appended to the copy of string. If start is less than one, the value one is used for start.
Case(ii): For a reference of the form
REPLACE(string,start,finish,substring)
the characters in the copy of string between positions start and finish, including those at start and finish, are deleted and replaced by the characters of substring. If start is less than one, the value one is used for start. If finish is greater than LEN(string, the value LEN(string) is used for finish. If finish is less than start, the characters of substring are inserted before the character at start and no characters are deleted.
Case(iii): For a reference of the form
REPLACE(string,target,substring,every,back)
the copy of string is searched for occurrences of target. The search is done in the backward direction if the argument back is present with the value true, and in the forward direction otherwise. If target is found, it is replaced by substring. If every is present with the value true, the search and replace is continued from the character following target in the search direction specified until all occurrences of target in the copy string are replaced; otherwise only the first occurrence of target is replaced.
REMOVE(string,start,finish
shall be provided.
Description: removes a specified substring from a string.
Arguments:
string - is either of type VARYING_STRING or type default CHARACTER,
start - is of type default INTEGER, and is OPTIONAL,
finish - is of type default INTEGER, and is OPTIONAL.
All arguments are scalars. The arguments are unchanged by the procedure.
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is a copy of the characters of string with the characters between positions start and finish, inclusive, removed. If start is absent or less than one, the value one is used for start. If finish is absent or greater than LEN(string, the value LEN(string) is used for finish. If finish is less than start, the characters of string are delivered unchanged as the result.
EXTRACT(string,start,finish)
shall be provided.
Description: extracts a specified substring from a string.
Arguments:
string - is either of type VARYING_STRING or type default CHARACTER,
start - is of type default INTEGER, and is OPTIONAL,
finish - is of type default INTEGER, and is OPTIONAL.
All arguments are scalars. The arguments are unchanged by the procedure.
Result Attributes: scalar of type VARYING_STRING.
Result Value: The result value is a copy of the characters of the argument string between positions start and finish, inclusive. If start is absent or less than one, the value one is used for start. If finish is absent or greater than LEN(string), the value LEN(string is used for finish. If finish is less than start, the result is a zero-length string.
CALL SPLIT(string,word,set,separator,back)
shall be provided.
Description: splits a string into a two substrings with the substrings separated by the occurrence of a character from a specified separator set.
Arguments:
string - is of type VARYING_STRING,
word - is of type VARYING_STRING,
set - is either of type VARYING_STRING or type default CHARACTER,
separator - is of type VARYING_STRING, and is OPTIONAL,
back - is of type default LOGICAL, and is OPTIONAL,
All arguments are scalar. The arguments set and back are unchanged by the procedure.
Action: The effect of the procedure is to divide the string at the first occurrence of a character that is in set. The string is searched in the forward direction unless back is present with the value true, in which case the search is in the backward direction. The characters passed over in the search are returned in the argument word and the remainder of the string, not including the separator character, is returned in the argument string. If no character from set is found or set is of zero length, the whole string is returned in word and string is returned as zero length. If the argument separator is present, the actual character found which separates the word from the remainder of the string is returned in separator. The effect of the procedure is such that, on return, either
word//separator//string
is the same as the initial string for a forward search, or
string//separator//word
is the same as the initial string for a backward search.
It should be noted that while every care has been taken by the technical working group to ensure that this module is a correct implementation of this part of ISO/IEC 1539 in valid Fortran code, no guarantee is given or implied that this code will produce correct results, or even that it will execute on any particular processor. Neither is there any implication that this illustrative module is in any way an optimal implementation of this standard; it is merely one fairly straightforward portable module that is known to provide a functionally conformant implementation on a few processors.
This annex includes links to some examples illustrating the use of facilities conformant with this part of ISO/IEC 1539. It should be noted that while every care has been taken by the technical working group to ensure that these example programs are a correct implementation of the stated problems using this part of ISO/IEC 1539 and in valid Fortran code, no guarantee is given or implied that this code will produce correct results, or even that it will execute on any particular processor.
The first example performs a word count. Note, it is not claimed that this program is the best way to code this problem, nor even that it is a good way, merely that it is a way of solving this simple problem using the facilities defined by use of the facilities defined in this part of ISO/IEC 1539.
A second and rather more realistic example is one which extends the above trivial example by producing a full vocabulary list along with frequency of occurrence for each different word. Again there is no claim that this is in anyway an optimal coding of this problem. It is merely an example that uses some of the facilities defined by this part of ISO/IEC 1539.