Macro definitions and functions

The following resources are from the bit employment class ：

#define Perform find replace ,#if You can distinguish whether to compile ,#undef You can de define , That is to cancel #define Macro defined things ,#end No such thing , Only #endif, So choose D.

The first three are commonly used macros , Namely ： Print the file 、 Print compile time 、 Print compilation date . besides , also __LINE__（ Line number ）、FUNCTION（ Function name ） Isochromatic , and __MAIN__ There is no such thing as , So choose D

Conceptual questions , This method is to solve the problem that the same file contains the same header file repeatedly , choose A.

Y(5+1) After replacement, it is ((N+2)*5+1), among N yes 4, So the result is 31,2 * (4 + 31) The result is 70, choose D.

macro C The preprocessed code is ：2+2*3+3, namely 2+6+3, be equal to 11, choose B.

Macro has no execution speed , It is to find and replace , choose C.A Macro is to find and replace , Cannot set recursive jump condition , Nature cannot recurse .B Macro is to find and replace , No execution , Type is impossible to talk about .D The essence of macro is directly stated in . So as long as you know that the macro is to find and replace , Other problems are not problems .

A Is a macro definition ,C It's a complex precompiled sentence , But it has nothing to do with the conditions ,D It is misused , Conditional compilation instructions include #if、#ifdef,#ifndef,#else,#elif、#endif etc. . In addition to that #if defined(xxx) Usage of . So choose B.

AB It's the opposite , Angle brackets are to go directly to the library to find , Double quotation marks are used to find... From the current directory first , Then go to the library to find .C Option header files cannot define global variables , Otherwise, if there are multiple files , That link will conflict . So choose D.D It's not perfect , In the development of large projects , This is not a good programming habit , It's better to put the classification in different header files and name them according to their characteristics , Because it is more convenient for code management and maintenance , For now , It's a good habit .