Thread: This compiles but gives error

This is a program i coded which parses command line arguments which are expected to be text files and in turn send contents to STDOUT which is screen.

it compiles but doesn't work. although it compiles. sinces its run from the commandline, i dont know how to debug such programs. can anyone tell me how to do this? i mean how to debug command line arguments.

this is the source code for the program;

Code:

#include <stdio.h>


void filecopy(FILE *, FILE *);
int main(int argc, char *argv[]){
    FILE *fp;
    if (argc == 1){
        filecopy(stdin, stdout);
    }
    else
       while (--argc > 0)
            if ( (fopen(*++argv, "r")) == NULL ){
                printf("could not open file: %s", *argv);
                continue;
            }
            else {
                filecopy(fp, stdout);
                fclose(fp);
            }


    return 0;

}


void filecopy(FILE *ifp, FILE *ofp){
    int c;
    if (ifp == NULL || ofp == NULL)
        return;
    else
        while ( (c = getc(ifp)) != EOF)
        putc(c, ofp);
}

Originally Posted by stahta01

I have never seen good code that decremented argc.
Or incremented argv.

You need to get out more! It's extremely common, and perfectly legal, of course.

Anyway, OP, you forgot to assign the file pointer to fp when opening the files.

Originally Posted by algorism

You need to get out more! It's extremely common, and perfectly legal, of course.

Anyway, OP, you forgot to assign the file pointer to fp when opening the files.

except i don't understand what you mean, but i believe this line assigns the file pointer to fp

Code:

if ((fp = fopen(*++argv, "r")) == NULL) {

Code:

#include <stdio.h>


void filecopy(FILE *, FILE *);
int main(int argc, char *argv[]){
    FILE *fp;
    if (argc == 1){
        filecopy(stdin, stdout);
    }
    else
      while(--argc > 0)
        if ((fp = fopen(*++argv, "r")) == NULL) {
            printf("cat: can't open %s\n", *argv);
            return 1;
        } else {
            filecopy(fp, stdout);
            fclose(fp);
        }
        return 0;
}


void filecopy(FILE *ifp, FILE *ofp){
    int c;
    if (ifp == NULL || ofp == NULL)
        return;
    else
        while ( (c = getc(ifp)) != EOF)
        putc(c, ofp);
}

this is complete code and still doesn't wokr

It seems to work for me.

How exactly are you calling the function?

Jim