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C programming, why does this large array declaration produce a segmentation fault?

This is my first time here so sorry if I break some rules or if this has been answered before.
I recently made a C program in which I had a matrix of

char buff[NR][1024*1024];

I needed NR = 128. So the program would alocate 128MB. This was in main(). I tried it on a few systems with enough memory with no error on compile. At runtime I recieved segmentation fault on all systems. It worked for NR = 7, but not 8.
I moved that code outside of main making it global. It didn’t crash anymore even for 128.
Does anyone know why this happened?
The compiler was GCC

Answer 1

The problem is you are overflowing the stack which is typically just a few MB in size (the exact size depends on the system and your compiler options). You could allocate the memory on the heap instead using malloc.