Writing to a file and console in C

Question

I am trying to write a function that allows me to write to the console and a file in C.

I have the following code but i realized that it does not allow me to append arguments (like printf).

#include <stdio.h>

int footprint (FILE *outfile, char inarray[]) {
    printf("%s", inarray[]);
    fprintf(outfile, "%s", inarray[]);
}

int main (int argc, char *argv[]) {

    FILE *outfile;
    char *mode = "a+";
    char outputFilename[] = "/tmp/footprint.log";
    outfile = fopen(outputFilename, mode);

    char bigfoot[] = "It Smells!\n";
    int howbad = 10;

    footprint(outfile, "\n--------\n");

    /* then i realized that i can't send the arguments to fn:footprints */
    footprint(outfile, "%s %i",bigfoot, howbad); /* error here! I can't send bigfoot and howbad*/

    return 0;
}

I'm stuck here. Any tips? For the arguments which I want to sent to function:footprints, it will consist of strings, chars and integers.

Are there other printf or fprintf fns that I can try to create a wrapper around?

Thanks and hope to hear ya'll responses.

See http://stackoverflow.com/questions/1719784/c-programming-forward-variable-argument-list. — Bill, Jan 05 '11 at 09:15

CB Bailey · Accepted Answer · 2011-01-05T09:22:11.363

5

You can use <stdarg.h> functionality and vprintf and vfprintf. E.g.

void footprint (FILE * restrict outfile, const char * restrict format, ...) {

    va_list ap1, ap2;

    va_start(ap1, format);
    va_copy(ap2, ap1);

    vprintf(format, ap1);
    vfprintf(outfile, format, ap2);

    va_end(ap2);
    va_end(ap1);
}

edited Jan 05 '11 at 09:22

answered Jan 05 '11 at 09:16

CB Bailey

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+1 but probably better for fooprint to take two arguments plus the var args; the file and the format like fprintf so that he can actually specify the format string (otherwise even tho you have a var arg function, you can only ever specify one var :/ – Jason Coco Jan 05 '11 at 09:19
@Jason Coco: Essential, it was at total mess up on my part. Fixed now. – CB Bailey Jan 05 '11 at 09:22

score 0 · Answer 2 · answered Jan 05 '11 at 09:16

0

printf, scanf etc. functions use variable length argument. Here is tutorial on how you can create your own function to take variable length arguments.

answered Jan 05 '11 at 09:16

taskinoor

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score 0 · Answer 3 · answered Jan 05 '11 at 09:17

Yes, there are several versions of printf. The one you're looking for is probably vfprintf:

int vfprintf(FILE *stream, const char *format, va_list ap);

Functions like printf need to be variadic functions (ie: taking a dynamic number of parameters).

Here an example:

int print( FILE *outfile, char *format, ... ) {
    va_list args;
    va_start (args, format);
    printf( outfil, format, args );
    va_end (args);
}

Note that this takes exactly the only parameters as printf: you can't print an integer array directly with this.

score -1 · Answer 4 · answered Jan 05 '11 at 09:17

You could pass in a char point that points to your string?

e.g. (syntax not checked but to give you an idea)

    #include <stdio.h>

int footprint (FILE *outfile, char * inarray) {
    printf("%s", inarray);
    fprintf(outfile, "%s", inarray);
}

int main (int argc, char *argv[]) {

    FILE *outfile;
    char *mode = "a+";
    char outputFilename[] = "/tmp/footprint.log";
    outfile = fopen(outputFilename, mode);

    char bigfoot[] = "It Smells!\n";
    int howbad = 10;

    //footprint(outfile, "\n--------\n");
    char newString[255];
    sprintf(newString,"%s %i",bigfoot, howbad);

    footprint(outfile, newString); 

    return 0;
}

Thanks, Clockwork Bear! I assume you're not Swiss. :) It would defeat my purpose of replacing the print_to_file and console if I adopted the sprintf function followed by the footprint function. — Poliquin, Jan 06 '11 at 09:11

Writing to a file and console in C

4 Answers4