fseek does not work with empty file

Question

I have the following code:

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

    FILE *fp;

    if(argc != 2){
        perror("Please specify a file");
        return 1;
    }

    if((fp=fopen(argv[1], "rb")) == 0){
        perror("File not found!");
        return 2;
    }

    int a = fseek(fp, 1000, SEEK_CUR);

    if(a<0){
        printf("fail\n");
    }

    fclose(fp);

    return 0;
}

When I call this with an empty binary file, no error occurs, eve though I would expect fseek() to return with -1. Does anyone know why is this not happening?

This is by design. If you invoke an `fwrite(string, 1, strlen(string), fp)` call after the `fseek` call in your program, the file will get padded with 1000 null chars before the string. — selbie, Feb 08 '15 at 20:02

score 1 · Accepted Answer · answered Feb 08 '15 at 20:07

1

From the documentation of fseek

POSIX allows seeking beyond the existing end of file. If an output is performed after this seek, any read from the gap will return zero bytes. Where supported by the filesystem, this creates a sparse file.

answered Feb 08 '15 at 20:07

Mike Nakis

56,297
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score 0 · Answer 2 · answered Feb 08 '15 at 20:01

0

That is correct. fseek do not fail when you seek past end-of-file.

answered Feb 08 '15 at 20:01

StenSoft

9,369
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fseek does not work with empty file

2 Answers2