Compilation and operation of program

Catalog

​ Edit one 、 Program translation environment and execution environment

1.C There are two environments for language code to run  

2. One C Compilation and running process of program

Two 、 compile

1. Preprocessing

2. compile

3. assembly

3、 ... and 、 link

1. link

2. Symbol summary

Four 、 The execution environment of the program

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One 、 Program translation environment and execution environment

1.C There are two environments for language code to run  

• 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. One C Compilation and running process of program

• 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 the programmer's personal library , Link the functions it needs to the program

Two 、 compile

Compilation is divided into preprocessing 、 Compilation and assembly are three processes

The following program contains two files , I will explain the compilation process of this program in detail

test.c

int Add(int a, int b)
{
    return a + b;
}

function.c

#define A 20
#include<stdio.h>
int b = 10;
int main()
{
    int a = A;
    
    int c = Add(a, b);
    printf("%d", c);
    // Addition operation 
    return 0;
}

1. Preprocessing

For details of preprocessing instructions, see ：(9 Bar message ) Preprocessing instruction _ Smart Knight blog -CSDN Blog

Preprocessing will perform a series of operations on the code to facilitate subsequent compilation , Generate .i file

The program mainly completes three tasks in the preprocessing stage ： The header file contains 、 Delete all #define And replace all macros and identifier constants 、 Delete all conditional compilation instructions 、 Delete all comments 、 Add line number and file ID 、 Retain #pragma Instructions

The effect is as follows ：

test.c

int Add(int a, int b)
{
    return a + b;
}

function.c

……   Here is stdio.h The content of 
#define Be deleted 
int b = 10;
int main()
{
    int a = 20;A Be replaced 
    
    int c = Add(a, b);
    printf("%d", c);
     The following comments have been deleted 

    return 0;
}

2. compile

Lexical analysis of the preprocessed code 、 Syntax analysis 、 Semantic analysis 、 Symbol aggregation and subsequent optimization produce the corresponding assembly language , Generate .s file .

Here we mainly talk about symbol summary , Symbol summary is mainly about the function names in the preprocessing code 、 The global variables are counted and made into a table .

test.o	function.o
b（ Global variables ）	Add（ Function name ）
main（ Function name ）
Add（ Function name ）

When you link later, you can check whether the function is correctly defined through this table

3. assembly

Convert assembly language into binary instructions , Generated at this time .o Only the computer can understand the document

The resulting test.o and function.o

3、 ... and 、 link

1. link

In the link phase, two operations, merging segment table and symbol summary, will be performed to form an executable program .

Merge segment tables ： The compiler will combine the data in the same format in multiple object files generated in the assembly stage , Finally form an executable program .

In the process of compiling Links , The change of file suffix is different ：

• stay windows In the system , Changes in documents ：.c -> .obj -> .exe（ The three steps of compilation are usually completed in one step ）
• stay linux In the system , Changes in documents ：.c -> .i ->.s -> .o -> .out

2. Symbol summary

Exists in even one table Add Function name , The linker will confirm which position is the definition of the function , If not , The compilation of this program will make mistakes . therefore , Linking is a step that the machine can check whether a function is undefined .

test.o	function.o
b（ Global variables ）	Add（ Function name ）（ After checking, this is the definition ）
main（ Function name ）
Add（ Function name ）

Four 、 The execution environment of the program

The process of program execution ：

• The program must be loaded into memory . In an operating system environment ： This is usually done by the operating system . In an independent environment , The loading of the program must be arranged manually , It can also be done by putting executable code into read-only memory .
• The execution of the procedure begins . And then I call main function .
• Start executing program code . At this point, the program will use a runtime stack （stack）, Store function local variables and return address .
• Programs can also use static （static） Memory , Variables stored in static memory retain their values throughout the execution of the program .
• To terminate the program . Normal termination main function ; It could be an accidental termination .