C++ Cookbook

1.19. Defining a Macro

Problem

You want to define the preprocessor symbol name, assigning it either an unspecified value or the value value.

Solution

The compiler options for defining a macro from the command line are shown in Table 1-16. Instructions for defining a macro from your IDE are given in Table 1-17. To define a macro using Boost.Build, simply add a property of the form <define>name[=value] to your target’s requirements, as shown in Table 1-15 and Example 1-12.

Table 1-16. Defining a macro from the command line

Toolset	Option
All	-D name [= value ]

Table 1-17. Defining a macro from your IDE

IDE	Configuration
Visual C++	From your project’s property pages, go to Configuration Properties → C/C++ → Preprocessor and enter name[=value] under Preprocessor Definitions, using semicolons to separate multiple entries.
CodeWarrior	From the Target Settings Window, go to Language Settings → C/C++ Preprocessor and enter: #define name[ = value] in the area labeled Prefix Text.
C++Builder	From Project Options, go to Directories/Conditionals and enter name[=value] under Preprocessor Definitions, using semicolons to separate multiple entries.
Dev-C++	From Project Options, select Parameters and enter: -D name[ = value] under C++ Compiler.

Discussion

Preprocessor symbols are used frequently in C++ source code to allow a single collection of source files to be used with several build configurations or operating systems. For example, suppose you want to write a function that checks ...