Question

I want to allocate memory and fill it to the pointer, that are one of the function parameter, but I think that I don’t get some important thing, help me please.

So, If I do that everything works fine:

void alloc(char **p, int n)
{
*p = new char[n];
}

int main() {
char * ptr = NULL;
int n = 10;
alloc(&ptr, n);
for(int i = 0; i<(n - 1); i++)
    ptr[i] = '1';
ptr[n - 1] = '\0';

printf("%s", ptr);
return 0;
}

Now I want to initialize the allocated memory also into the function

void alloc(char **p, int n)
{
*p = new char[n];
for(int i = 0; i<(n - 1); i++)
    *p[i] = '1';
*p[n - 1] = '\0';
} 

int main() {
char * ptr = NULL;
int n = 10;
alloc(&ptr, n); 
printf("%s", ptr);
return 0;
}

Program crashes. I don’t get why. Please, can someone explain?

Answer 1

Try (*p)[i] and (*p)[n - 1] instead. The precedence rules cause *p[i] to be evaluated as *(p[i]).