How do you override a defined macro?

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Chetan Santha

Professional Tutor with 15 years of experience.

We can use the #ifdef and #undef directive to undefine a previously defined macro.
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#define MYMACRO(x) x*x //previously defined macro ... #ifdef MYMACRO #undef MYMACRO #define MYMACRO(x) x*x*x //new definition #endif int main() { printf("%d\n", MYMACRO(2)); return 0; }
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You can't. The command line is handled before any source and header files. If a source file defines a macro, then it must not be defined before, and will get the new value from now on. The only way to change it, is to #undef and #define it again, at a later point. If you have access to a header...
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You can't. The command line is handled before any source and header files. If a source file defines a macro, then it must not be defined before, and will get the new value from now on. The only way to change it, is to #undef and #define it again, at a later point. If you have access to a header that is included after the definition, then you have a chance. read less
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Science Expert, C & C++ Strong

You can use the #undef preprocessor directive to undefine (override) a previously defined macro. Many programmers like to ensure that their applications are using their own terms when defining symbols such as TRUE and FALSE. Your program can check to see whether these symbols have been defined already,...
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You can use the #undef preprocessor directive to undefine (override) a previously defined macro. Many programmers like to ensure that their applications are using their own terms when defining symbols such as TRUE and FALSE. Your program can check to see whether these symbols have been defined already, and if they have, you can override them with your own definitions of TRUE and FALSE. read less
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How do you override a defined macro? in C programming How do you override a defined macro? You can use the #undef preprocessor directive to undefine (override) a previously defined macro. Many programmers like to ensure that their applications are using their own terms when defining symbols such as...
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How do you override a defined macro? in C programming How do you override a defined macro? You can use the #undef preprocessor directive to undefine (override) a previously defined macro. Many programmers like to ensure that their applications are using their own terms when defining symbols such as TRUE and FALSE. Your program can check to see whether these symbols have been defined already, and if they have, you can override them with your own definitions of TRUE and FALSE. The following portion of code shows how this task can be accomplished: ... #ifdef TRUE /* Check to see if TRUE has been defined yet */ #undef TRUE /* If so, undefine it */ #endif #define TRUE 1 /* Define TRUE the way we want it defined */ #ifdef FALSE /* Check to see if FALSE has been defined yet */ #undef FALSE /* If so, undefine it */ #endif #define FALSE !TRUE /* Define FALSE the way we want it defined */ ... In the preceding example, the symbols TRUE and FALSE are checked to see whether they have been defined yet. If so, they are undefined, or overridden, using the #undef preprocessor directive, and they are redefined in the desired manner. If you were to eliminate the #undef statements in the preceding example, the compiler would warn you that you have multiple definitions of the same symbol. By using this technique, you can avoid this warning and ensure that your programs are using valid symbol definitions. read less
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Yes, You can use the #undef preprocessor directive to undefine (override) a previously defined macro
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Computer & Maths Professor

You can use the #undef preprocessor directive to undefine (override) a previously defined macro.
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C and linux Expert

You can use the #undef preprocessor directive to undefine (override) a previously defined macro. Many programmers like to ensure that their applications are using their own terms when defining symbols such as TRUE and FALSE.
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LearnHowToLearn, Expert In Programming Languages

Just redefine it.
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LearnHowToLearn, Expert In Programming Languages

#undef first the already defined macro and then redefine it. # define
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