Precompilation in the C language

Conditional compilation mainly has the following several situations, in view of forgetting several times, hereby write down, hope to remember .... Scenario 1:

#if XX

Code snippet 1#else Code snippet 2
#endif如果XX为真则执行代码段1否则执行代码段2. Case 2: #ifdef XX code snippet 1#else code snippet 2#endif If the xx is defined then execute code snippet 1 otherwise execute code Snippet 2. Case 3: #ifndef x Code snippet 1#else code snippet 2#ENDIF If no x is defined execute code snippet 1 otherwise execute code Snippet 2.

Precompilation in the C language