Why are two strings with same content different while using wchar_t?

Question

I am writing a code for comparing two strings of type LPSTR and wchar_t type. The contents of strings are same but the output is showing that the strings are different. Below is screenshot of the complete code.

#include <iostream>
#include <string.h>
#include <wtypes.h>
using namespace std;
int main(int argc, char** argv) 
{
    LPSTR str1= "Abcdef123456";
    wchar_t *str2 = L"Abcdef123456";
    if(!strcmp((char *)str1, (char *)str2))
    {
        cout<<"same";   
    }
    else
    {
            cout<<"diff";
    }

    return 0;
}

Upon execution, the output is diff. I think the output should be same. Please help.

Your call to`strcmp` is comparing single byte characters. The first string is composed of single byte characters, the second of wide 2-byte characters. They are not the same thing. You need to convert the strings to the same storage format before you do the comparison. — Baldrick, Mar 08 '17 at 14:15
If `"A"` and `L"A"` had been the same, why would we need two versions? — Bo Persson, Mar 08 '17 at 14:23
@DeiDei I thought that since the contents are same, the strings should be same. But now I know the difference between the two strorage types. — akashagrawal, Mar 09 '17 at 05:40

eerorika · Accepted Answer · 2017-03-10T22:39:19.757

1

L'A' has a different representation in memory than 'A'. If you pretend that an array of wchar_t is an array of char (by explicit conversion char*) and compare it to another array of char with different representation, they will compare different.

The output is as expected.

A correct way to compare the strings is to convert the narrow string to a wide string. That isn't exactly trivial to do correctly, so here is an example:

auto length = std::strlen(str1);
std::wstring temp(length, L'\0');
std::mbstowcs(&temp[0], str1, length);
if (!wcscmp(temp.c_str(), str2))
   // ...

edited Mar 10 '17 at 22:39

answered Mar 08 '17 at 14:35

eerorika

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Thanks @user2079303 for the solution, this works for me. Please also explain me what `wstring temp(length, L'\0')` does here. – akashagrawal Mar 09 '17 at 05:32
@akashagrawal it constructs a wide string object for the buffer where the narrow string is converted into. – eerorika Mar 09 '17 at 08:14
Hey thank you so much @user2079303 . The code works but now the problem is that on debugging, hovering over `str2` shows the string value whereas hovering on `c_str()` does not show the value of string. Also, due to this, the conditional part is not working properly. Please help me with that. – akashagrawal Mar 09 '17 at 13:06
@akashagrawal I used wrong length originally. That should be fixed now. If you would like to see the content of a string object in a debugger, you should contact the sales team of your debugger provider. – eerorika Mar 10 '17 at 22:40

Why are two strings with same content different while using wchar_t?

1 Answers1