为什么在使用 qsort() 函数时会出现 munmap_chunk(): invalid pointer Aborted？

Question

I got this error "munmap_chunk(): invalid pointer Aborted" when I using qsort() to sort a array that contains class objects. Here is my code:

#include <iostream>
#include <string>
#include <cstdlib>

class MyString : public string
{
 public:
    MyString(const char *str) :string(str) {}
    MyString(const string & str) :string(str) {}
};

int CompareString(const void * e1, const void * e2)
{
    MyString * s1 = (MyString *) e1;
    MyString * s2 = (MyString *) e2;
    if ( *s1 < *s2 ) return -1;
    else if ( *s1 == *s2 ) return 0;
    else if ( *s1 > *s2 ) return 1; 
}

int main()
{
    MyString SArray[4] = {"big","me","about","take"};
    qsort(SArray,4,sizeof(MyString), CompareString);
    for( int i = 0;i < 4;++i )
        cout << SArray[i] << endl;
    return 0;
}

When I comment out the qsort() line. The error disappears. I want to know why this happened and how to solve the error.

My output:

me

abo

bi

take

munmap_chunk(): invalid pointer

Aborted

Answer 1

qsort works by copying elements around, but it does so by calling memcpy . This is undefined behaviour for non-POD types (such as std::string ), hence your crash.

Solution: use std::sort instead, which is the C++ way of sorting things.