malloc-ating multidimensional array in function

Question

I\'m trying to allocate a 2d array in a C program. It works fine in the main function like this (as explained here):

#include 
#include 

        

Answer 1

C is pass by value. And to sum up the error you are doing, this example should be helpful -

void foo( int *temp )
{
     temp = malloc(sizeof(int)) ;
     // temp is assigned to point to new location but the actual variable
     // passed from main do not point to the location temp is pointing to.

     *temp = 10 ;
}

int main()
{
     int *ptr ;
     foo( ptr ) ;

     // ptr is still unintialized
     *ptr = 5 ; // Segmentation fault or Undefined behavior

     return 0;
}

So, instead you should do -

void foo( int **temp )
{
    *temp = malloc(sizeof (int) );
    // ...
}

And now call the function as foo(&ptr); in the main() function.