调用free（）时出现分段错误

Question

I'm building some modular function and I'm not getting why I get a segmentation fault after freeing my module.

My .h file

void StringInit(String *this, char const *s)
{
    this->str = strdup(s);
    printf("%s\n", this->str);
}

void StringDestroy(String *this)
{
    if(this == NULL || this->str == NULL)
        return;
    this->str = NULL;
    free(this);
}

int main()
{
    char          *str;
    String        test;

    str = "hello\n";
    StringInit(&test, str);
    StringDestroy(&test);
    return(0);
}

Answer 1

You have to call free for this->str , not for this (because you allocated a new string with strdup ). Moreover set a member to NULL doesn't free it:

if (this == NULL || this->str == NULL)
    return;

free(this->str);
this->str = NULL;

Everything else in your code works as expected, you can allocate objects on stack (just remember you don't need to free them).

Answer 2

free should be used to free pointers that have been allocated using malloc . Your test string has been allocated on the stack . As Alfe points out:

String*  test = (String*)malloc(sizeof(String));
StringInit(test, str);
StringDestroy(test);

And as Adriano's answer points out, you've also allocated a new string with strdup . Seems like there are a myriad of issues here!