Precompiled Headers & Normal C++ Semantics
By Jeffrey Taylor, October 01, 2001
If arranged correctly, precompiled headers, like those in Visual C++, can double the build speed. However, it is possible also to arrange precompiled header files in a manner that is inconsistent with normal C++ semantics.
Oct01: Precompiled Headers & Normal C++ Semantics
<b>(a)</b> pch.h
// Solaris JUST includes this file.
#include <iostream.h>
<b>(b)</b> pch,cpp
// Visual C++ puts the start of this file into the
// precompiled header.
#define STR1 "Charlie "
#include "pch.h"
#define STR2 "Daniels"
<b>(c)</b> main.cpp
#include "pch.h"
#ifndef STR1
# define STR1 "James "
#endif
#ifndef STR2
# define STR2 "Brown"
#endif
int main()
{
cout << STR1;
cout << STR2;
return 0;
}
Example 1: This program has different behaviors on NT and UNIX: (a) pch.h; (b) pch.cpp; (c) main.cpp.
