How to detect insufficient disk space when using stdio operations in C / C ++?

Question

I am doing a small program as follows:

void reserve_file_space(char* file_path, size_t amount)
{
    FILE* fp = fopen(file_path, "w+b");
    if(!fp)
    {
        printf("could not create a new file\n");
        return;
    }

    int fseek_ret = fseek(fp, amount, SEEK_SET);
    if(fseek_ret != 0)
    {
        printf("could not seek to the desired position\n");
        fclose(fp);
        return;
    }

    char garbage = 1;
    size_t ret = fwrite(&garbage, 1, 1, fp);
    if(ret != 1)
    {
        printf("could not write the garbage character\n");
    }

    fclose(fp);
}

int main(int argc, char* argv[])
{
    reserve_file_space("C:\\Users\\SysPart\\Desktop\\test.bin", 1 << 30);
    return 0;
}

The free space on my PC is about 500 MB. In main(), if I call reserve_file_space("C:\\Users\\SysPart\\Desktop\\test.bin", 1 << 28 /*256 MB*/);, it produces a file created with an exact size of 256 MB. However, if I call reserve_file_space("C:\\Users\\SysPart\\Desktop\\test.bin", 1 << 30 /*1 GB*/);, it produces an output file of size 0 and does not produce any error messages.

How do I know if there is enough free disk space?

Answer 1

How can I find out if there is enough free disk space?

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POSIX statvfs().

WinAPI GetDiskFreeSpace().