HP UX Fortran Software manual File handling, Example 27 Example 8-7 passchars.f90

Example 27 Example 8-7 pass_chars.f90

PROGRAM main

!This program passes to character variables to a C routine,

!which overwrites them. This program displays the

!character variables before and after the call.

!Initialize the character variables and append null

!characters so that C can process them. CHARACTER(LEN=10) :: first_name = "Pete"//CHAR(0) CHARACTER(LEN=15) :: last_name = "Seeger"//CHAR(0)

!Note that character variables, like arrays, are passed by

!reference in both languages. There’s no need to use the

!%REF built-in function, so long as the C routine

!provides an extra argument for the "hidden" length

!parameter. To suppress passing that parameter, use %REF. CALL get_string(first_name, last_name)

PRINT 20, first_name, last_name

20 FORMAT(/, 'The names passed back to Fortran: ', A, 1X, A) END PROGRAM main

Example 28 Example 8-8 get_string.c

#include <stdio.h> #include <string.h>

void fix_string_for_f90(char s[], int len);

/* get_string: overwrites the string arguments fname and lname;

*fname_len and lname_len are the hidden length arguments, which

*are implicitly passed by Fortran with each string argument.

*/

void get_string(char fname[], char lname[], int fname_len, int lname_len)

{

printf(“The names passed to C: %s %s\n", fname, lname);

printf(“\nEnter the first and last names of a banjo player: "); scanf(“%s%s”, fname, lname);

fix_string_for_f90(fname, fname_len); fix_string_for_f90(lname, lname_len);

}

/* fix_string_for_f90: replaces the null at the end of the string

*in the character array and th a blank and blank fills the

*remaining elements up to len; this processing is necessary if

*the character variable is to be manipulated by Fortran

*/

void fix_string_for_f90(char s[], int len)

{

int i;

for (i = strlen(s); i < len; i++) s[i] = ' ';

}

Below are the command lines to compile, link, and execute the program, followed by the output from a sample run.

$ cc -Aa -c get_string.c

$ f90 pass_chars.f90 get_string.o $ a.out

The names passed to C: Pete Seeger

Enter the first and last names of a banjo player: Wade Ward

The names passed back to Fortran: Wade Ward

File handling

A Fortran unit number cannot be passed to a C routine to perform I/O on the associated file; nor can a C file pointer be used by a Fortran routine. However, a file created by a program written

120 Calling C routines from HP Fortran