Question

I am attempting to compile and run a test C program in Xcode. This program reads 5 symbols from a text file and closes it. The program builds successfully, but when I try to run the program I get the error: GDB: Program received signal: “EXC_BAD_ACCESS” around fclose(in).

#include <iostream>
#include <unistd.h>

int main (int argc, const char * argv[])
{
    bool b;
    char inpath[PATH_MAX];
    printf("Enter input file path :\r\n");
    std::cin >> inpath;
    FILE *in = fopen(inpath, "r+w");
    char buf[5];
    fread(&buf,sizeof(buf),5,in);
    printf(buf);
    fclose(in);
    return 0;
}

What could be a cause of this?

Answer 1

Ah! sizeof(buf) will return 5, so you’re asking for 25 bytes in a 5-byte buffer. This overwrites auto storage and clobbers in.

And, of course, note that fprint(buf) will be attempting to print a buffer with no terminating null, so it will print garbage beyond the end of what was read.