Unsigned long long int 作为 C 中一个非常大数组的数组索引

Question

I need a very big array to represent a series of points. To be more exact I need 256 * UINT_MAX points that have x and y values between 0 and 1. What I've tried so far is this but when I try to access array[i] my program crashes. What I can use to iterate through that array and to allocate that memory? Thank you!

unsigned long long int N = (unsigned long long int) 256 * (unsigned long long int) UINT_MAX;
float** array = (float**) malloc( N * sizeof(float*));
    
for(unsigned long long int i = 0; i < N; i++)
{
      array[i] = (float*)malloc(2 * sizeof(float));
      printf("Allocated");
      array[i][0] = (float) rand() / RAND_MAX;
      array[i][1] = (float) rand() / RAND_MAX;
        
}

Answer 1

Your programs crashes because you try to allocate a HUGE amount of memory you likely do not have (without checking the result of malloc is NULL ). Indeed, UINT_MAX is close to 4e9 on many mainstream system and so you try to allocate at least 8 * 256 * 4e9 = 8 TB of memory (without taking into account allocation in the loop that will be insanely slow)!

Answer 2

Assuming you're on a 64-bit platform, then it's likely that

        UINT_MAX == 4294967295
sizeof (float *) == 8

so you are trying to allocate 8 terabytes of memory in one chunk, which is almost certainly failing. Check the return value of malloc to make sure it isn't NULL .

Why do you think you need to allocate that large an array? What kind of data are you trying to model?