c macro faqs

Question: What is the difference between a string copy (strcpy) and a memory copy (memcpy)? When should each be used?
Answer: The strcpy() function is designed to work exclusively with strings. It copies each byte of the source string to the destination string and stops when the terminating null character () has been moved. On the other hand, the memcpy () function is designed to work with any type of data. Because not all data ends with a null character, you must provide the memcpy () function with the number of bytes you want to copy from the source to the destination.

Question: How can you check to see whether a symbol is defined?
Answer: You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined
(#ifdef) or whether it has not been defined (#ifndef).


Question: How do you override a defined macro?
Answer: You can use the #undef preprocessor directive to undefine (override) a previously defined macro.

Question: What is #line used for?
Answer: The #line preprocessor directive is used to reset the values of the _ _LINE_ _ and _ _FILE_ _ symbols,
respectively. This directive is commonly used in fourth-generation languages that generate C language source files.

Question: What is a pragma?
Answer :The #pragma preprocessor directive allows each compiler to implement compiler-specific features that can be turned on and off with the #pragma statement. For instance, your compiler might support a feature called loop optimization. This feature can be invoked as a command-line option or as a #pragma directive.

To implement this option using the #pragma directive, you would put the following line into your code:

#pragma loop_opt(on)
Conversely, you can turn off loop optimization by inserting the following line into your code:

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