C++ content of std::string

sizeof std::string is 4, this is to say it has only a member variable i.e, a pointer to content buffer.

 

 

}:cat tt.C
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

#include <iostream>
using namespace std;

void foo(std::string &str)
{
        //printf("%s/n",NULL);  // To generate a core file
        int * p = (int *)&str;

        printf("sizeof(std::string) is %d/n",sizeof(str));
        printf("*(p+0)=0x%x/n",(*p));
        printf("*(*(p+0))='%s'/n",(char *)((*(p+0))));
        //printf("*(p+1)=0x%x/n",(*(p+1)));
        //printf("*(*(p+1))=%s/n",(char *)((*(p+1))));
}

int main()
{
        std::string ss("12345");
        foo(ss);
        return 0;
}

 

 

 

It will get following output:

}:./a.out
sizeof(std::string) is 4
*(p+0)=0x40e10
*(*(p+0))='12345'