Learn C Function by Example 3 : Name of function cannot be global predefined macro

Basic Note :
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• Global predefined macro starts with underscore. (_) .
• We cannot use Global predefined macro as our function name.

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Example : Some of the predefined macros in C
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• __TIME__
• __DATE__
• __FILE__
• __LINE__

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Learn by Program : Valid Example

#include<stdio.h>
void __FILE__();
int main()
{
   __FILE__();
}
void __FILE__(){
   printf("Hello World");
}

Output :

Compile error

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We can have valid function names starting with underscore -
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• _add()
• _getTime()
• _calsum()

[/checklist] Note :

Try to avoid using underscore as first character .

Why we should avoid to use underscore as first character ?
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• Using underscore as first character is perfectly legal in C.
• But in C we have many more different predefined constants and macros starting with underscore.
• It will create confusion between user defined and predefined identifier.
• so prefer not to use underscore as first character in writing function.

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