


C Pre-processors for Eliminating Conditional Blocks
In the realm of C programming, the need often arises to eliminate dead code based on defined or undefined macros. While the standard C pre-processor provides limited conditional compilation capabilities, advanced requirements demand specialized tools. This article explores a C pre-processor capable of fulfilling such a need.
Consider the scenario where a codebase contains conditional blocks such as:
#ifdef NAME1 #define ALBUQUERQUE "ambidextrous" #else #define PHANTASMAGORIA "ghostly" #endif
A pre-processor with the desired functionality would accept command-line arguments to specify defined or undefined macros, such as '-DNAME1' or '-UNAME1'. Running the command with '-DNAME1' would generate the following output:
#define ALBUQUERQUE "ambidextrous"
On the other hand, executing the command with '-UNAME1' would produce:
#define PHANTASMAGORIA "ghostly"
More complex scenarios with multiple conditions and nested blocks can also be handled accurately. Consider the following example:
#ifdef USE_VOID #ifdef PLATFORM1 #define VOID void #else #undef VOID typedef void VOID; #endif /* PLATFORM1 */ typedef void * VOIDPTR; #else typedef mint VOID; typedef char * VOIDPTR; #endif /* USE_VOID */
Running the command with '-DUSE_VOID -UPLATFORM1' would result in the following output:
#undef VOID typedef void VOID; typedef void * VOIDPTR;
Finally, an example involving nested conditions:
#ifndef DOUBLEPAD #if (defined NT) || (defined OLDUNIX) #define DOUBLEPAD 8 #else #define DOUBLEPAD 0 #endif /* NT */ #endif /* !DOUBLEPAD */
Passing the argument '-UOLDUNIX' would produce:
#ifndef DOUBLEPAD #if (defined NT) #define DOUBLEPAD 8 #else #define DOUBLEPAD 0 #endif /* NT */ #endif /* !DOUBLEPAD */
Recommended Solution
Based on the recommendations provided in the original thread, sunifdef stands out as a robust and effective pre-processor capable of eliminating dead code based on defined/undefined macros. It has been extensively used with great success, eliminating thousands of unnecessary conditional blocks.
The above is the detailed content of How Can a C Pre-processor Eliminate Dead Code Based on Defined/Undefined Macros?. For more information, please follow other related articles on the PHP Chinese website!

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