Question

I know segmentation fault means that the process has attempted to access certain memory that it’s not allowed to.

I’m running some program written by others using C++. And when my input is large (around 1GB), there’ll be a segmentation fault even though I requested 30GB memory; while when input size is quite small, it goes well.

So what shall I do? Is it because there’s not enough memory? I’m really kind of a newbie without much knowledge of C++. I don’t even know which part of the code controls memory allocation.

Thanks to BLender, line from the debugging is:

Program received signal SIGSEGV, Segmentation fault.
0x0000003fbd653174 in _IO_vfscanf_internal ()
from /share/bin/intel/cc/10.1.015/lib/tls/x86_64/libc.so.6

Answer 1

Your code calls malloc several times, but never free, so it uses quite a lot of memory. And it never checks for an out-of-memory condition…

My suggestion is that you change all the calls to malloc to something like:

size_t total_memory = 0;
void *my_malloc(size_t sz)
{
    void *res = malloc(sz);
    total_memory += sz;
    if (res == NULL)
    {
        printf("Too much memory eaten: %zu\n", total_memory);
        abort();
    }
    return res;
}
#define malloc(x) my_malloc(x)

And see what happens.