fgetc() adds carriage return to line feed

Question

I'm trying to make a program that concatenates multiple files to one. The code that i currently have is the following:

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

void main(int n, char** args) {
    if (n < 2) printf("Too few arguments. Format: <output> [files...]");

    FILE* output = fopen(args[1], "w");

    for (int i = 2; i < n; i++) {
        FILE* curr = fopen(args[i], "rb");

        while (!feof(curr)) {
            int c = fgetc(curr);

            fputc(c, output);
        }

        fclose(curr);
    }

    fclose(output);
}

But, when I have \n in a file, fgetc adds \r behind the \n in the new file. I've tried to open the file as binary, but it still adds the additional \r behind all \n-s.

How do I get rid of this functionality?

fopen(..., "r") remove the "b" for text mode (rather than binary mode). — pmg
– pmg, Commented Feb 6, 2021 at 12:23
stackoverflow.com/a/28462221/4756299 would work here And this is likely a dupe of that question... — Andrew Henle
– Andrew Henle, Commented Feb 6, 2021 at 12:26
@pmg But if this is on a POSIX system, text mode won't help. — Andrew Henle
– Andrew Henle, Commented Feb 6, 2021 at 12:26
while (!feof(curr)) {...} <<-- don't do this! stackoverflow.com/questions/5431941/… — wildplasser
– wildplasser, Commented Feb 6, 2021 at 12:42
Title is fgets(), yet code is fgetc(). What is the true goal? — chux
– chux, Commented Feb 6, 2021 at 13:33

chqrlie · Accepted Answer · 2021-02-06 21:26:01Z

Since you open the input files in binary mode ("rb"), you get the CR/LF end-of-line sequences as separate bytes '\r' and '\n', which get stored into the output files as sequences of CR/CR/LF on legacy systems, because the output file opened in text mode converts '\n' as CR/LF and stores '\r' unchanged as CR.

Just open the output file in binary mode as well, with "wb".

Also fix some other problems as shown here:

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

int main(int argc, char **argv) {
    if (argc < 2) {
        fprintf(stderr, "Missing arguments. Format: <output> [files...]\n");
        return 2;
    }

    FILE *output = fopen(argv[1], "wb");
    if (output == NULL) {
        fprintf(stderr, "Cannot open output file '%s': %s\n",
                argv[1], strerror(errno));
        return 1;
    }

    for (int i = 2; i < argc; i++) {
        int c;
        FILE *curr = fopen(argv[i], "rb");
        if (curr == NULL) {
            fprintf(stderr, "Cannot open input file '%s': %s\n",
                    argv[i], strerror(errno));
            continue;
        }
        while ((c = fgetc(curr)) != EOF) {
            fputc(c, output);
        }
        fclose(curr);
    }

    fclose(output);
    return 0;
}

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