List of articles

•  @[TOC]( List of articles )
•   One 、 The translation environment of the program （ Compile and link ）
•   Two 、 The running environment of the program

One 、 The translation environment of the program （ Compile and link ）

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

• The first is the translation environment , In this environment, the source code is converted into executable machine instructions .
• The second is the execution environment , It's used to actually execute code .

Here's the picture ： This is the general process of our compiler compiling a source file into an executable file

• Each source file that makes up a program （test.c） Through the compilation process, they are converted into object code （test.obj）
• Each target file is linked by a linker （linker） Tied together , Form a single and complete executable program .
• The linker will also introduce standards c Any function in the function library used by the program .

For a source file （test.c） Become the final binary file （test.exe） It can be simply represented by the following figure ：


Looking at the picture, we know ： The compilation is divided into three steps ：

1. precompile （ Preprocessing ）(test.c —>test.i)
   （1） Deal with all the comments , Replace... With a space
   （2） Will all #define Delete , And expand all macro definitions
   （3） Processing conditional compilation instructions #if、#ifdef、#elif、#else、#endif
   （4） Handle #include, Expand the included files
   （5） Keep what the compiler needs to use #pragma Instructions
2. compile (test.i —>test.s)
   （1） hold C Compile language code into assembly code
   （2） Grammatical analysis , Lexical analysis , Semantic analysis , Symbols are summarized to form a symbol table
3. assembly (test.s —>test.o)
   Assembly process actually refers to the process of translating assembly language code into target machine instructions . For each... Processed by the translation system C Language source , Will eventually get the corresponding target file through this processing . What is stored in the object file is the machine language code of the object equivalent to the source program .

After compiling, execute the link , What will links do ？

1. Merge segment tables
2. Symbol table merging and symbol table relocation
3. In the end （test.exe）

Two 、 The running environment of the program

1. The program must be loaded into memory , In an operating system environment ： Usually this is 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 .
2. The execution of the procedure begins , Then call main function .
3. Start executing program code , At this point, the program will use a runtime stack , Store function local variables and return address , The program also uses static （static） Memory , Variables stored in static memory retain their values throughout the execution of the program .
4. To terminate the program . Normal termination main function , It may also be an accidental termination （ Code error ）