GCC introduction

View version   gcc/g++ -v/--version

gcc Workflow

1. precompile （ Source code ：.c .c++ .h）：gcc -E main.c -o main.i
2. compile （ Source code after preprocessing ：.i）：gcc -S main.i -o main.s
3. assembly （ Assembly code ：.s）：gcc -c main.s -o main.o
4. link （ Object code ：.o, Startup code , Library code , Other object codes ）：gcc main.o -o main

• precompile ： Delete all “#define”, And expand all macro definitions , Process all conditional precompiled instructions at the same time , Then process “#include” Preprocessing instruction , Insert the included file into the location of the precompiled instruction , Delete all comments , Add line number and filename ID , The compiler generates symbol information for debugging and displays line numbers when compiling errors and warnings , Last but not least “#pragma” Compiler Directives , Its function is to set the state of the compiler or instruct the compiler to complete some specific actions .
• Compile phase ： Lexical analysis 、 Syntax analysis 、 Semantic analysis , Code optimization , Summary symbol , Generate assembly code .
• Assembly stage ： Translate assembly instructions into binary format , Generate each section, Generate symbol table .
• Link phase ： Merge each section, adjustment section Initial displacement and segment size , Merge symbol tables , Perform symbol parsing , Assign virtual addresses to symbols , Symbol repositioning .

gcc and g++ difference

1. The suffix is .c Of ,gcc Think of it as C Program , and g++ As if c++ Program
2. The suffix is .cpp Of , Both of them will think that C++ Program
3. Compile phase ,g++ Would call gcc, But in the link phase , Because of the need C++ The library of , So here we need to use g++ To complete the link .
4. about “_cplusplus” macro , It indicates that the compiler will press C still C++ Grammar to explain , therefore , If the suffix is .c, And adopt gcc compiler , Then the macro is undefined , otherwise , Is defined .

gcc Parameter options

Compilation options	explain
-o test test.c / test.c -o test	take test.c Compile to executable test
-I directory	Appoint include Search directory containing files
-g	Generate debug information at compile time
-D	Specify a macro at compile time
-w	No warning messages are generated
-W	Generate all warning messages
-On	Optimization options ,-O0 No optimization ,-O1 Is the default value ,-O3 The highest level of optimization
-l	When the program is compiled , Specify the library to use
-L	Specify when compiling , Search the path to the library
-fPIC/fpic	Generate location independent code
-shared	Generate shared object file , It's usually used when building shared libraries
-std	Appoint C standard