Why a smiley is displayed instead of a username? - c++

Question

Why a smiley is displayed instead of a username?
Changing console properties did not help...
#include "pch.h"
#include <windows.h>
#include <Lmcons.h>
#include <string>
#include <iostream>
std::string UserName() {
TCHAR username[UNLEN + 1];
DWORD size = UNLEN + 1;
std::string UserName1;
UserName1 = GetUserName((TCHAR*)username, &size);
std::cout << UserName1 << std::endl;
return UserName1;
}
int main()
{
UserName();
}
Conclusion: ☺

Answer 1

Have a look at the MSDN documentation of that function. The signature is
BOOL GetUserNameA(
LPSTR lpBuffer,
LPDWORD pcbBuffer
);
The function's return value is a BOOL, which is non-zero if the function succeeded. It does not return a string. The username buffer you pass to the lpBuffer parameter will contain the username:
std::string UserName() {
char username[UNLEN + 1];
DWORD size = UNLEN + 1;
std::string UserName1;
if (GetUserNameA(username, &size))
UserName1.assign(username, size-1);
std::cout << UserName1 << std::endl;
return UserName1;
}
As to why it displays a smiley, the reason is quite simple: the function happens to return TRUE, which is a 1 on your platform. A BOOL is an int, and this can be coerced to a char. Thus, the compiler calls the operator=(char) method on your std::string, writing char 0x01 to the std::string and setting its length to 1:
The string value is set to a single copy of this character (the string length becomes 1).
To recap, you're assigning character code 0x01 to your std::string. I assume you're running your code in a Windows Command Prompt, which uses an encoding derived from DOS' codepage 437. Here is its character map:
The upper left corner is code 0. What do you see right next to it? (tip: after 0 comes 1).
P.S.: On Windows, you can type any character of CP437 by holding down Alt and typing the character code. Alt + 1 will give you the smiley you got by running your program.