malloc(): memory corruption

Question

Here is the simplified program that I think can lead to this error.

char *p = (char*)malloc(8192);
for(int i = 0; i < 9200; ++i){
  p[i] = '1';
}
char *s = (char*)malloc(strlen(p)); 

The original project is rather complicated, so I simplified it. I assigned 8192 bytes using malloc. Then my program will write more than 8192 characters in to the array. Then I will allocate memory using malloc.

This mini program didn't crash. But in the original big project, it crashes with this error:

malloc(): memory corruption: 0x0000000007d20bd0 ***

What may cause this difference?

Answer 1

It is undefined behavior because you have allocated 8192 bytes memory but you are trying to write 9200 bytes. Which is out of bound.