SIGSEGV with STL string

[system]

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <algorithm>
#include <vector>
#include <string>
#include <map>
#include <sstream>
#include <string.h>
using namespace std;
struct node {
        string s;
        int a;
};
int main()
{
        int i, j, k;
        string s;
        struct node *st, t;
        st = ( struct node * )malloc( sizeof( struct node ) );

    st->a = 2;
    st->s = "SDAD";

    return 0;
}

it gives segmentation fault due to st->s = "SDAD". why ?

edit : using new instead of malloc, it worked fine.

[TripleM_sof]

malloc does not call any constructors, and in particular doesn't call the string constructor. st->s is therefore just garbage; you can't call the = operator on it.

That's why you should use new instead.