Char pointer return wrong value with clang

I´m trying to execute a program where I return a char * using malloc with clang but it gives me some errors that with mingw it doesn´t give me.

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *prueba(const char *);

int main(){

    printf("%s\n", prueba("adedds"));
    printf("%s\n", prueba("vxbc"));
    printf("%s\n", prueba("ewefxx"));
    printf("%s\n", prueba("asde"));
    printf("%s\n", prueba("vbcvbcv"));
    printf("%s\n", prueba("sded"));

}

char *prueba(const char *str){

    char *str_return = malloc(strlen(str));
    for (size_t i = 0; i < strlen(str); i++) str_return[i] = str[i];
    return str_return;
}

The results with clang are these:

adeddsð
vxbc└
ewefxxð
asde└
vbcvbcv
sded└

The results with mingw are these:

adedds
vxbc
ewefxx
asde
vbcvbcv
sded

I´m newbie with this compiler so I don´t know what really happen

>Solution :

You forgot to zero terminate your strings

int len = strlen(str);
char *str_return = malloc(len + 1); <<<<== make space for 0
for (size_t i = 0; i < len; i++)
      str_return[i] = str[i];
str_return[len] = 0; <<<<<========   set 0
return str_return;

simpler is

int len = strlen(str);
char *str_return = malloc(len + 1); <<<<== make space for 0
strcpy(str_return, str);
return str_return;

also strdup will do it in one got for you, it combines malloc and copy

return strdup(str);

and of course you should really check that malloc workd