C language-Use of module programming and extern

Modular programming:

We can all see that the programs written by others are neat, standardized, and readable. Not all programs and functions unload a main file, but the entire project is subdivided clearly below, high portability.

Modularize a program or function with independent overall functions into another file, and manage it in a unified manner. Finally, the program is called in an orderly manner under # include "xxxx. h" in the main file.

The following describes how to modularize the program:

1. Create a head file named "people. h" and add the following content:

# Ifndef _ lele__h _ // pre-compiled header file ifndef => if no define, if the project does not define this all // file, use the _ PEOPLE__H _ constant to judge

# Define _ lele__h _ // If the header file "people. h" is not defined, it can be defined. If the header file is already defined, the header file will not be compiled // translated.

// Function declaration

Char * run ();

Void say (char * str );

Void eat (char str []);

Int calculate (int a, int B );

# Endif // end character

2. Create a people. c file. Let's use the people. h function declaration in the file and add the following content:

# Include "people. h"

# Include "app. h"

# Include <string. h>

// Function implementation

Char * run ()

{

Discance = 100; // change the value of the extern variable, that is, change the value of the extern variable.

Char * ch = "he has runned about ";

Return ch;

}

Void say (char * str)

{

Printf ("I said ");

While (* str! = NULL)

{

Printf ("% c", * (str ++ ));

}

Printf ("\ n ");

}

Void eat (char str [])

{

Char * p = str;

Printf ("I am eating ");

While (* p! = NULL)

{

Printf ("% c", * (p ++ ));

}

Printf ("\ n ");

}

Int calculate (int a, int B)

{

Int sum;

Sum = a * B;

Return sum;

}

3. This completes the ing between a pair of C (source file) and H (header file.

Next, let's take a look at the use of extern. We create a header file app. h and add the following content:

# Include <stdio. h>

Extern int discance; // It can only be declared here and cannot be initialized. Otherwise, it will be wrong.

4. Finally, we will write the most familiar main file:

# Include "app. h"

# Include "people. h"

// Re-define and initialize to prove that this external variable is under the current data file,

// If app. h is introduced externally, sum can be used to change the value of sum,

// It is equivalent to changing the value in the current file.

Int discance = 0;

Void main ()

{

Char * p;

Printf ("Welcome to modular programming \ n ");

Eat ("meat ");

Say ("hello world ");

P = run ();

While (* p! = NULL)

{

Printf ("% c", * (p ++ ));

}

Printf ("% d meter! \ N ", discance );

}

In this way, simple Modular programming is completed, and it doesn't matter if you don't understand it. You can download the source file and run it on VC. There are C and C ++ versions, you can make a comparison.

This article is from the "I am a driver-MyWay" blog, please be sure to keep this source http://dragonyeah.blog.51cto.com/7022634/1285921