calloc function generating zeros instead of memory addresses-CodePudding

I'm trying to create a graph with 264346 positions. Would you know why calloc when it reaches 26,000 positions it stops generating memory addresses (ex: 89413216) and starts generating zeros (0) and then all the processes on my computer crash?

The calloc function should generate zeros but not at this position on my code.

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <time.h>
#include <string.h>
#include <limits.h>



int maxV;


struct grafo {
    int NumTotalVertices;
    int NumVertices;
    int NumArestas;
    int **p;
};
typedef struct grafo MGrafo;

MGrafo* Aloca_grafo(int NVertices);


int main(){
    MGrafo *MatrizGrafo;
    MatrizGrafo = Aloca_grafo(264346);

    return 0;
}


MGrafo* Aloca_grafo(int NVertices) {
    int i, k;
    MGrafo *Grafo ;
    Grafo = (MGrafo*) malloc(sizeof(MGrafo)); 
    Grafo->p = (int **) malloc(NVertices*sizeof(int*)); 
    
    for(i=0; i<NVertices 1; i  ){
        Grafo->p[i] = (int*) calloc(NVertices,sizeof(int));// error at this point
        //printf("%d - (%d)\n", i, Grafo->p[i]); // see impression
    }
    printf("%d - (%d)\n", i, Grafo->p[i]);
    Grafo->NumTotalVertices = NVertices; 
    Grafo->NumArestas = 0; 
    Grafo->NumVertices = 0;
    return Grafo;
}

CodePudding user response：

You surely dont mean what you have in your code

Grafo = (MGrafo*)malloc(sizeof(MGrafo));
Grafo->p = (int**)malloc(NVertices * sizeof(int*)); <<<<=== 264000 int pointers

for (i = 0; i < NVertices   1; i  ) {  <<<<< for each of those 264000 int pointers
    Grafo->p[i] = (int*)calloc(NVertices, sizeof(int)); <<<<<=== allocate 264000 ints

I ran this on my machine

its fans turned on, meaning it was trying very very hard
after the inner loop got to only 32000 it had already allocated 33 gb of memory

I think you only need to allocate one set of integers, since I cant tell what you are trying to do it hard to know which to remove, but this is creating a 2d array 264000 by 264000 which is huge (~70billion = ~280gb of memory), surely you dont mean that

OK taking a comment from below, maybe you do mean it

If this is what you really want then you are going to need a very chunky computer and a lot of time.

Plus you are definitely going to have to test the return from those calloc and malloc calls to make sure that every alloc works.

A lot of the time you will see answers on SO saying 'check the return from malloc' but in fact most modern OS with modern hardware will rarely fail memory allocations. But here you are pushing the edge, test every one.

'Generating zeros' is how calloc tells you it failed.

https://linux.die.net/man/3/calloc

Return Value The malloc() and calloc() functions return a pointer to the allocated memory that is suitably aligned for any kind of variable. On error, these functions return NULL. NULL may also be returned by a successful call to malloc() with a size of zero, or by a successful call to calloc() with nmemb or size equal to zero.