krm - 1 year ago 51

C Question

I'm wondering how could I know if malloc did it's job?

Is there a way I could check if I'm using malloc properly?

Printing the matrix values addresses will tell me something other than been contiguous?

`int main (int argc, char ** argv)`

{

int x,y;// int variables

char str[100];//char variable

/*Variable pointer to pointer long long int type*/

int ** matrix;//matrix 3X6

/*We alocate memory for the first matrices dimension (rows)*/

matrix= malloc(3 * sizeof(*matrix));

/*We alocate memory for the second matrices dimension (columns)*/

for(x=0; x<6; x++){

matrix[x]=malloc(6 * sizeof(int));

}

/* Matrix initialization*/

for(y=0;y<3;y++){ // row matrix iterations

for(x=0;x<6;x++)//columns matrix iterations

{

matrix[y][x]=x;// assign value

}

}

/*Print each matrix position value*/

sprintf(str, "\nMatrix\n");

write(1, str, strlen(str));

for(int y=0; y<3; y++){

for(int x=0; x<6; x++){

sprintf(str,"[%d][%d]=%d ", y , x, matrix[y][x]);

write(1, str, strlen(str));

}

sprintf(str, "\n");

write(1, str, strlen(str));

}

exit(0);

}

Answer Source

`malloc`

and other dynamic memory allocation functions return a pointer to the memory you allocated when they suceed, or `NULL`

if they failed or you called them with a nonsensical value (like doing `malloc(0)`

or somesuch).

From the manual page on `malloc`

:

[...] 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. [...]

For your code, add a simple check against null to see if your `malloc`

succeeded:

```
for(x=0; x<6; x++){
matrix[x]=malloc(6 * sizeof(int));
if (matrix[x] == NULL) {
printf("Dynamic memory allocation failed");
//dostuff
}
}
```