CODEWITHSUNDEEP
c++
Legion
Legion

Reputation: 3447

_getch returns extra null terminators

I got this function from a tutorial

void read( char* buf, int maxSize ) {
   const char* const pEnd = buf + maxSize;
   for ( char c = _getch(); c != 13 && (buf + 1 < pEnd); c = _getch(), buf++ ) {
      _putch( c );
      *buf = c;
   }
   *buf = 0;
}

It filled buf with null terminators after each character was entered.

I had to modify it like this to make it work:

void read( char* buf, int maxSize ) {
    const char* const pEnd = buf + maxSize;
    char c = 0;

    while ( c != 13 && (buf < pEnd) ) {
        c = _getch();
        if ( c != 0 ) {
            _putch( c );
            *buf = c;
            buf++;
        }
    }

    *buf = 0;
}

What is wrong with _getch()? Why does it return null terminators constantly? Even in the working function if I step through it, I can see _getch() returning '\0' 3 or 4 times after each character is typed.

EDIT -- I'm using Visual Studio 2017. While this looks like C code, it's because the tutorial series starts by teaching cstrings before moving on to std::string.

Upvotes: 0

Views: 336

Answers (1)

Legion
Legion

Reputation: 3447

It turns out there's a bug in Visual Studio 2017 with _getch() which causes null terminators to be inserted after every character. If you switch from debug to release mode the bug goes away.

See here: https://developercommunity.visualstudio.com/content/problem/252047/something-wrong-with-getch-in-loops.html

Upvotes: 1

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