What Are Precompiled Headers (pch.h) and How Do They Speed Up Compilation?

Precompiled Headers (pch.h) in Programming

A precompiled header, often denoted as "pch.h," is an essential part of optimizing compilation times in C and C development. It plays a significant role in reducing compilation time, particularly for large header files or those included in multiple translation units.

What is pch.h?

A precompiled header is an intermediate form of a header file that the compiler processes more efficiently. Normally, a compiler must parse and process every header file included in a source code file. However, with precompiled headers, the compiler does this processing only once for the precompiled header.

Why Include pch.h as the First Header File?

Including "pch.h" as the first header file in a source code allows the compiler to take advantage of the precompiled header. By placing it at the beginning, the compiler immediately encounters the precompiled header and skips any other declarations or includes before that.

In Visual Studio, the precompiled header is commonly named "pch.h" and can be configured through project settings. Compiling with the "/Yu" option instructs Visual Studio to not compile anything before the "#include "pch.h" statement. This assumes that all code up to and including that line is already precompiled.

Benefits of Using Precompiled Headers

Using precompiled headers offers significant benefits:

• Faster Compilation Times: By eliminating the need to repeatedly parse and process the same sections of code, precompiled headers drastically reduce compilation time.
• Improved Build Performance: Rebuilding projects becomes much faster as the precompiled header is already in place and does not need to be recompiled.
• Increased Productivity: Developers spend less time waiting for compilation to finish, allowing them to be more productive.

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