CODEWITHSUNDEEP
cfileprintingio
Thanasi Poulos
Thanasi Poulos

Reputation: 278

I'm getting a really odd timing error, where something is executing before I believe it should

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>

int c, n, E, b, s, v, t, opt, valid = 0;
char current = '\0';
char previous = '\0';
FILE *fp;

/*  -n numbers lines
 *  -E appends a dollar sign to line ends
 *  -b numbers only non-blank lines
 *  -s squeezes multiple blank lines down to 1
 *  -v displays control chars, excluding tab
 *  -t includes tab in the above
 *  -e is the same as -E and -v
 */

int setFlags(int argc, char *argv[]) {
    int op;
    while ((op = getopt(argc, argv, "nEbsvte")) != -1) {
        switch (op) {
            case 'n': {
                n = 1;
                break;
            } case 'E': {
                E = 1;
                break;
            } case 'b': {
                b = 1;
                break;
            } case 's': {
                s = 1;
                break;
            } case 'v': {
                v = 1;
                break;
            } case 't': {
                t = 1;
                break;
            } case 'e': {
                E = 1;
                v = 1;
                break;
            } case '?': {
                //fprintf(stderr, "Option `-%c` is not valid.\n", optopt);
                return EXIT_FAILURE;
            } default: {
                abort();
            }
        }
    }
    opt = optind;

    if(n == 1) {
        b = 0;
    }

    return EXIT_SUCCESS;
}

int checkFile(char *path) {
    if (access(path, R_OK) == 0) {
        return EXIT_SUCCESS;
    } else {
        fprintf(stderr, "cat: %s: %s\n", argv[i], strerror(errno));
        errno = 0;
        return EXIT_FAILURE;
    }
}

int doPrint(char *path) {
    if (strcmp(path, "stdin") == 0) {
        fp = stdin;
    } else {
        if (checkFile(path) == 1) {
            return EXIT_FAILURE;
        } else {
            fp = fopen(path, "r");
        }
    }
    while ((c = fgetc(fp)) != EOF) {
        putchar(c);
    }
    fclose(fp);
    return EXIT_SUCCESS;
}

int main (int argc, char *argv[]) {
    if (setFlags(argc, argv) == 1) {
        fprintf(stderr, "The program has terminated with an error.\n"
        "An invalid option was specified.\n");
        return EXIT_FAILURE;
    } else {
        if ((argc - opt) == 0) {
            doPrint("stdin");
        } else {
            for(int i = opt; i < argc; i++) {
                doPrint(argv[i]);
            }
        }
    }
}

I'm getting a really crazy bug, where my program outputs the error line in checkFile, before it finishes writing the contents of the file (always one chat before the end).

It's driving me insane, and no matter where I move that piece of code, it doesn't work as intended.

I'm sure the answer is probably trivial, but it has me stumped. I'd even thrown in sleeps and various other things just before output finished, and it would throw the error, THEN sleep, THEN print the final character.

Any help?

Upvotes: 0

Views: 72

Answers (1)

acarlow
acarlow

Reputation: 924

When using printf, stdout output is buffered by default. This means it can be interleaved with other output, often from stderr. stderr is unbuffered by default so that it's output is printed immediately as would normally be desired when an error occurs.

Interleaving can be fixed with judicious use of fflush or by turning off file buffering of stdout using setbuf. Be sure to read the man pages for setbuf as there are some caveats.

In this case, adding fflush(stdout) at the end of the doPrint function should fix the "problem".

Upvotes: 2

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