Basic concepts of C + + program development

The development of a C + + program requires the following steps: Edit, compile, connect, run debugging. More specific is: source code → preprocessor → compiler → target code → linker → executable program.

1, Source code: Source program is not compiled according to a certain programming language specification written text files. In C + +, the file. cpp file that stores the source code.

2. Pre-processor: C Preprocessor is a macro-preprocessor (preprocessor), the main function of which is the inclusion of the header file (including files), the macro substitution (macros expansion), the conditional compilation ( conditional compilation), row control (line contral).

(1) source file contains (including files)

The file contains instructions to insert the contents of a file into the # include section.

Common file-containing formats:

A, #include <filename>: Find the filename file in the standard compiler include directory;

B, #include "filename": Now the current source file directory to find, if not found, and then to the standard directory to find.

To avoid multiple inclusions (double inclusion), use #include命令常常被强制同 # include guard or #pragma once.

For example:

File Grandfather.h

struct Foo {    int  menber;};

File Father.h

" Grandfather.h "

File child.c

" Grandfather.h "  "father.h"

At this point, the Grandfather.h file is included two times, and because the struct foo is defined two times, it will cause a compilation error. Solution to this problem:

A. Using # include Guards

Modify the Grandfather.h to:

#ifndef Grandfather_h #define Grandfather_h    struct  foo {    　　int  member;    }; #endif /*grandfather_h*/

B, using #pragma once

Modify the Grandfather.h to:

#pragma oncestruct  foo {    int  member;};

(2) Conditional compilation

By # If, #ifdef, #ifndef开始, then 0-n a #elif, followed by 0-1 #else, and finally with #endif. When # If, #ifdef, #ifndef后面的条件表达式为真时, the code is compiled with the same control logic as the If-else statement.

For example:

#include <iostream>usingnamespace  std; #define A 2int  main () {    #ifdef a    "Yes" << Endl;     #else       "No" << Endl;      #endif }

The running result of the program is "yes", and when the macro definition of a is commented out, the result is "No".

(3) macro definition

There are two types of macro definitions: Object-like and Function-like, the simple macro definition that we often call and the macro definition with parameters.

A, simple macro definition

#define <identifier> <replacement token list>

For example:

#define PI 3.1415

B, macro definition with parameters

#define <identifier> (<parameter list>) <replacement token list>

For example:

#define Squre (R) (3.14*R*R)

There are also line controls and user-defined errors in other preprocessing.

Reference documents:

[1] http://en.wikipedia.org/wiki/C_preprocessor;

[2] http://www.th7.cn/Program/cp/201403/182079.shtml.

Basic concepts of C + + program development