malloc
// if you initialize a pointer and want to use it like an array,
// you have to claim the space you use,
// that is what the memory-allocation-funtion (malloc) does;
// exaple for that: str(0) belongs to you, but str(1), str(2), ... do not
// if you do not use the malloc funtion;
// you can access it, but it could be used by another programm;
#include <stdio.h>
#include <stdlib.h>
void func(void)
{
char *str = malloc(sizeof(char) * 5); // sizeof --> char needs
// a specific space per value saved;
// *5 --> 5 is the number of values in the array;
char *str1 = malloc( 5 * sizeof *str1 );// |
char *str2 = malloc( sizeof(char[5]) );// | other syntaxes
if(str == NULL) { exit(1); } // malloc returns NULL
// if it could not allocate the memory;
str[0] = 'H';
*(str+1) = 'e'; // used like pointer
str[2] = 'y'; // used like array
*(str+3) = '!';
str[4] = '\0';
printf("%s\n", str);
free(str); // frees the memory allocated to str;
// if you free the memory too early and try to access str later
// that is called a memory leak;
}
int main(void)
{
func();
return 0;
}
// shell: Hey!
// improved version of Thurger's