C language program compilation

author ： A collection of old dreams 186

project ：C Language programming ---- Little bit's Growth Diary

 

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Preface ：

Today, Xiaobian will bring you to know c Compiling and linking the underlying logic of language

Catalog

1. Program translation environment and execution environment

2. Detailed compilation + link  

2.1 Translation environment

2.2 The compilation itself is also divided into several stages ： 

2.3 Running environment  

3. Pretreatment details  

3.1 Predefined symbols

3.2 #define

3.2.1 #define Define identifier

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1. Program translation environment and execution environment

stay ANSI C In any implementation of , There are two different environments

The first 1 One is the translation environment , In this environment, source code is converted into executable machine instructions .

The first 2 One is the execution environment , It's used to actually execute code

2. Detailed compilation + link  

When we write the code , And when mutating and linking , A black box will pop up , In our project directory, we will generate .exe Executable file , What we need to know now is how this thing is formed .

 

2.1 Translation environment

We can generally know that , The executable is compiled by 、 Link these two parts together to produce . It can be said in words ： Source file ( It can be more than one ) After the compiler compiles, the object file is generated , These target files are sent to the link library for linking , Thus, an executable program is generated .

 

 

Each source file constituting a program is converted into object code through the compilation process （object code）.

Each target file is linked by a linker （linker） Tied together , Form a single and complete executable program .

Linkers also introduce standards C Any function in the function library used by the program , And it can search individual programmers The library of , Link the functions it needs to the program

 

2.2 The compilation itself is also divided into several stages ： 

  One thing we need to pay attention to , The compilation process of the compiler is not just compilation .  in other words , Compilation itself can also be divided into several stages .

because Visual Studio These compilers are an integrated development environment , Therefore, it is not convenient to show the details of each part . But study later Linux In the process of , We can certainly observe it when we look back . Here I will explain in words .

1. In the precompile phase , The compiler will translate the contents of the header file 、define Defined text substitutions are written .i The file of , And delete the comments . in other words , Precompiled .i It's written in the document C The language code , Is all that includes header files C The language code .
2. Compile phase , From this stage , It is necessary to gradually enable computer hardware to recognize our code . So this stage will put C Translation of language code into assembly language code . For example, we have int max = 10; , Then the compilation phase will put int As a type, generate the corresponding assembly instructions ,max Is a variable name. , Generate the corresponding assembly statement , = It's the assignment symbol , Assembly statements will also be generated , wait …… These assembly codes are stored in .s In file .
3. assembly , Here are the steps to generate the target file . At this stage, the assembly code will be split in more detail , Generate the most primitive machine instructions , Binary instructions . These instructions will be placed in .obj The file of (Linux In the environment .o file ), stay Linux These binary instructions can be observed in the environment , But our brain will think these are garbled .
 

2.3 Running environment  

The process of program execution ：

1. The program must be loaded into memory . In an operating system environment ： This is usually done by the operating system . In an independent environment , Program

The loading of must be manually scheduled , It can also be done by putting executable code into read-only memory .

2. The execution of the procedure begins . And then I call main function .

3. Start executing program code . At this point, the program will use a runtime stack （

stack）, Store the local variables and return of the function Address . Programs can also use static （static） Memory , Variables stored in static memory are stored throughout the execution of the program Keep their values all the time .

4. To terminate the program . Normal termination main function ; It could be an accidental termination .

3. Pretreatment details  

3.1 Predefined symbols

__FILE__      // Source files to compile 
__LINE__     // The current line number of the file 
__DATE__    // The date the file was compiled 
__TIME__    // When the file was compiled 
__STDC__    // If the compiler follows ANSI C, Its value is 1, Otherwise, it is not defined 

These predefined symbols are built into the language .

  Take a chestnut ：

#include<stdio.h>
int main()
{
	FILE* p;
	p = fopen("test.txt", "w");
	if (p == NULL)
	{
		perror("open");
	}
	// Format output 
	fprintf(p, "file:%s line:%d date:%s time:%s\n", __FILE__, __LINE__, __DATE__,__TIME__);
	fclose(p);
	p = NULL;

	return 0;
}

 

3.2 #define

3.2.1 #define Define identifier

---

---

grammar ：

#define name stuff

 

#define MAX 1000
#define reg register          // by  register This keyword , Create a short name 
#define do_forever for(;;)     // Replace an implementation with a more vivid symbol 
#define CASE break;case        // Writing case Automatically put  break write .
//  If you define  stuff Too long , It can be divided into several lines , Except for the last line , Add a backslash after each line ( Line continuation operator ).
#define DEBUG_PRINT printf("file:%s\tline:%d\t \
                          date:%s\ttime:%s\n" ,\
                          __FILE__,__LINE__ ,       \
                          __DATE__,__TIME__ )  

put questions to ：

stay define When defining identifiers , Do you want to add... At the end ; ?

Better not add ;

such as ：

#include<stdio.h>
#define MAX 100;
int main()
{
	int n = 0;
	scanf("%d", &n);
	if (n > MAX)
	{
		n = MAX;
	}
	return 0;
}

  It should be noted that , When we define identifiers , Try not to add a semicolon after it , Because when we write code, we are used to adding semicolons , If there is a semicolon after the defined identifier , There may be imperceptible errors .

 

  Of course, we can also use this function to realize some elusive operations , Suppose a programmer uses swich In the sentence case , It's all about break, He felt very troublesome , Then he wrote such a piece of code ：

#define CASE break;case

#include <stdio.h>

int main()
{
	int n = 3;
	switch (n)
	{
	case 1:
		CASE 2 :
			CASE 3 :
			printf("hello world!\n");
		CASE 4 :
		break;
	}
	return 0;
}