CODEWITHSUNDEEP
c++
Yuri Dosovitsky
Yuri Dosovitsky

Reputation: 141

Bug in std::wstring?

I found some very strange behavior of std::wstring.

#include "stdafx.h"
#include <string>
#include <iostream>

int _tmain(int argc, _TCHAR* argv[])
{
    std::wstring someString = L"Some dummy string";

    std::wstring base1 = L"Base1 ";
    std::wstring base2 = L"Base2 ";
    std::wstring second = L"Second";

    base1 += second.at(0) + L" ";

    base2 += second.at(0);
    base2 += L" ";

    return 0;
}

The base1 and base2 output should be the same, but there are not. Base1 is actually doesn't work.

Any ideas?

Upvotes: 1

Views: 160

Answers (1)

Benjamin Lindley
Benjamin Lindley

Reputation: 103761

second.at(0) + L" "

This expression doesn't do what you expect. at(0) returns a wchar_t, which is really an integer. L" " is a wide string literal, which is implicitly converted to a wchar_t const*. So in the expression above, you are doing pointer arithmetic, adding whatever the value of L'S' is (probably the same as the ASCII value of S, which is 83, I believe). This gives you a pointer far outside the range of the string literal, which is only 2 characters. The end result is undefined behavior.

To get the effect you are probably going for, you can make one of your operands a wstring.

base1 += second.at(0) + std::wstring(L" ");

Probably simpler in this case would be to just use 2 statements.

base1 += second.at(0);
base1 += L' ';

Upvotes: 8

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