Question

I get a strange problem here, and ask for help.

(gdb) 
    28      set_file_bit( file, bytePos, bitPos, argv[1] );
    (gdb) p argv[1]
    $3 = 0xbfffef5c "00"
    (gdb) s
    set_file_bit (file=0x804b008, bytePos=2, bitPos=2, binary=0x80490e5 "11") at util/file.c:112
    112     long int pos = ftell(file);

We can see the value of binary is 0x80490e5, not 0xbfffef5c , why?
argv is the parameter of function main.
some part of function main is

int main( int argc, char** argv ){
    FILE* file = 0;
    file = fopen( "t.txt", "r+" );
    unsigned int bytePos = 2;
    unsigned int bitPos = 2;
    char buff[2] = { 0, 0 };
    get_byte( file, bytePos, 1, buff);
    set_file_bit( file, bytePos, bitPos, argv[1] );

Thanks

Answer 1

The most likely reason is that set_file_bit was compiled with optimization, and the parameters have not been completely set up when GDB stepped into it.

Try printing binary inside set_file_bit, it will likely be 0xbfffef5c. When debugging optimized code, one frequently sees such artifacts. Rebuild with -O0 to make your debugging easier.