C preprocessor: Difference between revisions
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The C preprocessor is a powerful tool and properly used may be very useful. |
The C preprocessor is a powerful tool and properly used may be very useful. |
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The following have been checked to work in GCC. |
The following have been checked to work in GCC. |
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=== Rules === |
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=== Uses === |
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==== Deleted Code ==== |
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A code block may be commented out to delete it from the program, however nesting deleted fragments may reduce legibility with C++ style comments, and C comments do not nest at all. |
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A better solution is to wrap the code in and #if 0-#endif block, where the conditional 0 means false : |
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[code] |
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#if 0 |
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print("memory state: "); |
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print(mem->state); |
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print("\nallocated blocks: "); |
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print(mem->allocs); |
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#endif |
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[/code] |
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Many editors, like [[VIm]] have by default syntax highlighting rules that treat such #if 0-#endif blocks as comments. |
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The #if-#endif directives must be balanced, single-quotes characters must balance etc. so for deleting non-code text use comments instead. |
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There is a number of counter-intuitive consequences of macros and macro expanding design. |
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[http://gcc.gnu.org/onlinedocs/cpp/Macro-Pitfalls.html#Macro-Pitfalls Macro Pitfalls] |
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== See also == |
== See also == |
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* [[C]] |
* [[C]] |
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Revision as of 14:46, 19 July 2008
C preprocessor
The C preprocessor is a powerful tool and properly used may be very useful. The following have been checked to work in GCC.
Rules
Uses
Uses for debugging
Deleted Code
A code block may be commented out to delete it from the program, however nesting deleted fragments may reduce legibility with C++ style comments, and C comments do not nest at all. A better solution is to wrap the code in and #if 0-#endif block, where the conditional 0 means false : [code]
- if 0
print("memory state: ");
print(mem->state);
print("\nallocated blocks: ");
print(mem->allocs);
- endif
[/code] Many editors, like VIm have by default syntax highlighting rules that treat such #if 0-#endif blocks as comments. The #if-#endif directives must be balanced, single-quotes characters must balance etc. so for deleting non-code text use comments instead.
Hazards of the C preprocessor
There is a number of counter-intuitive consequences of macros and macro expanding design. Macro Pitfalls
See also
External Links
The GNU C preprocessor manual: