Can a Preprocessor Eliminate Inactive C Code Based on Command-Line Macro Definitions?

Preprocessors with Selective Code Elimination for C

The provided C question seeks a preprocessor that removes inactive code blocks based on defined or undefined macro values specified via command-line arguments. Here's an analysis and a list of tools that meet this requirement:

Understanding the Issue

The preprocessor's default behavior is to incorporate all code sections, even if certain macros controlling their execution are undefined. This can lead to unnecessary code bloat and potential errors. The ideal solution would be a preprocessor that selectively eliminates these inactive blocks.

Solution: Son of Unifdef (sunifdef)

As suggested in the replies, Sunifdef is a powerful tool that aligns perfectly with the requirement. It allows users to specify which macros are defined or undefined using -D and -U options. It then analyzes the code and eliminates any sections that depend on the specified macros.

Example of Sunifdef in Action

Consider the following code snippet:

#ifdef MACRO1
    // Code specific to MACRO1 defined
#else
    // Code specific to MACRO1 undefined
#endif

Running sunifdef with -D MACRO1 will output only the code specific to MACRO1 being defined, effectively removing the inactive branch.

Other Tools

While Sunifdef is a popular choice, it's not the only available tool. Other options include:

• Unifdef: An older preprocessor that serves a similar purpose but lacks regular updates.
• Coan: A successor to Unifdef with improved capabilities.

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