c - Mallocing char* with same length as another char* causes it become a copy? -

i trying write simple c program creates struct char* field , assigns have same value argv[1]. want create char* same length argv[1], reason data inside contains same value argv[1]. here code far:

#include <stdlib.h> #include <stdio.h> #include <string.h> #include <ctype.h>  struct example{     char *str; };  struct example* create(char *s){     struct example *p = (struct example*)malloc(sizeof(struct example));     char * copy = (char*)malloc(strlen(s));     strcpy(copy, s);     p->str = copy;     free(copy);     return p; }  void new_char(struct example * t){     printf("original: %s\n", t->str);     char *w = (char *)malloc(strlen(t->str));     printf("why copy? %s\n", w);     free(w); }  void clean(struct example *t){     free(t); }  int main(int argc, char **argv){     struct example * p = create(argv[1]);     new_char(p);     clean(p);     return 0; } 

then when compile , run program using gcc 6.1, out put

> gcc -wall -g -o test test.c > ./test "test value here" > original: test value here > why copy? test value here 

this code wrong

struct example* create(char *s){     struct example *p = (struct example*)malloc(sizeof(struct example));     char * copy = (char*)malloc(strlen(s));     strcpy(copy, s);     p->str = copy;     free(copy);     return p; } 

first need allocate strlen + 1

second cannot free 'copy' here, p->str points @ it, have dangling pointer. copy , malloc use strdup http://linux.die.net/man/3/strdup

struct example* create(char *s){     struct example *p = (struct example*)malloc(sizeof(struct example));     p->str = strdup(s);     return p; } 

the reason got same string because released string heap , got again when called malloc, purely luck, time might crash, garbage,...