Most of our programmers are probably from C Language learning , Tens of thousands of lines , Hundreds of thousands of lines , Even millions of lines of code , But do you all know C The whole process of language compilation , If not clear , I'll take you all together today to make a decryption .
C Language is a high-level language compared with assembly language , To run on the system , It needs to be converted into executable code that can be read by the machine through the compiler .
with Linux On system gcc take as an example , Usually we compile a source file with the following command ：
$gcc hello.c –o hello
After compilation , It will be generated in the directory hello This program , Run it directly to see the results .
but hello How is this program generated , In fact, there are several steps in the process . Recompile with the following command , You can see all the intermediate files .
$gcc -save-temps hello.c –o hello
hello hello.c hello.i hello.o hello.s
C The compiling process of compiler is divided into four steps ：
1） Pretreatment Pre-prosssing
Preprocessing generated hello.i Intermediate file of , Mainly completed the following steps ：
Remove all comments
Expand all macro definitions （ That is, character substitution ）
insert #include Contents of the document
Handle all conditional compilation
hello.i The contents of the document are as follows （ Large file size , Only the bottom part is shown ）：
You can find that all comments in the source code have been deleted , And inserted stdio.h Content of header file .
2） compile Compiling
Compilation will hello.i File compilation generates an intermediate file hello.s, You can see that there are assembly languages inside , So the purpose of compilation is to convert the source code into assembly language .
3） assembly Assembly
Assembler will hello.s Compiled into hello.o file .hello.o It's binary , It's all machine executable code .
4） connect Linking
Connection, as the name suggests, plays a connecting role , although hello.o It's already binary , But there's something inside, like printf
Function needs to call another library . Connector makes a binding between our binary and other libraries . You can see the generated hello Files are better than hello.o Much bigger .
Come here C The complete compilation process of is over , The examples in this article are Linux operating system , The compiler uses gcc, But in other operating systems , such as
Unix,Windows, Or use another compiler , The principle is the same , Interested students can learn the principles of compilation , A deeper understanding of compilation .