c - Why does this dynamic allocation of type char** and char* using malloc segfault? -

i don't understand why code segmentation faults. can work if define char** inside of function, allocate char**, point *commandsarray @ char**. can explain not understanding? in advance.

#include <stdio.h> #include <stdlib.h> #include <string.h>  void input_str_to_sngl_commands( char*** commandsarray );  int main() {      char** commandsarray_var;     input_str_to_sngl_commands( &commandsarray_var );  return 0; }  void input_str_to_sngl_commands( char*** commandsarray ) {     *commandsarray = (char**) malloc(2*sizeof(char**));     *commandsarray[0] = (char*) malloc(30*sizeof(char));     *commandsarray[1] = (char*)malloc(30*sizeof(char)); } 

you got precedence wrong: [] has higher precedence *, *commandsarray[1] accesses wrong address.

use parentheses force evaluation order, this

*commandsarray = malloc(2*sizeof(char*)); (*commandsarray)[0] = malloc(30*sizeof(char)); (*commandsarray)[1] = malloc(30*sizeof(char)); 

or use temporary variable use more readable syntax:

char** ret = malloc(2*sizeof(char*)); ret[0] = malloc(30*sizeof(char)); ret[1] = malloc(30*sizeof(char)); *commandsarray = ret; 

demo.

note: casting malloc unnecessary.