GCC usage, makefile summary

---

Preface

I've been playing a game recently , To use C Programming , I used to use integration before IDE Conduct C Programming for , For the use of gcc,g++ It is true to compile code directly. I don't know , Learn about the relevant use , And learned some basic makefile Grammatical knowledge , Write a work summary

---

One 、gcc Use

https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Overall-Options.html#Overall-Options
Official documents

see gcc edition

gcc --version

No compilation options

compile .c file , And link it into an executable file . Default output name a.out, Output the file to the current directory .

gcc main.c

Options -o

Specify the name of the output file

gcc main.c -o main.o

Options -E

Stop after the pretreatment stage ; Do not run the compiler . The output is in the form of preprocessed source code , Send to standard output . It will generate .i Final document

The preprocessing function mainly includes macro definition , File contains , Conditional compilation , To comment, etc .
The preprocessing instruction is based on # The line of code that begins with the .
file.c: Must be pretreated C Source code .
file.i: Should not be pretreated C Source code .
file.ii: Should not be pretreated C++ Source code .

gcc -E main.c -o main.i

Options -S

Compile into assembly language without linking

gcc -S main.c -o main.s

gcc -S main.i -o main.s 

Options -c

Compile the file to the target file , But don't link

gcc -c main.c -o main.o

Link to generate executable

Will all .o File links , Generate executable files , The default dynamic link

gcc main.o test.o -c main #  Link the target file 
gcc main.c test.c -o main # Generate executable file in one step 

-static This option takes a static link to the generated file

gcc main.c test.c -o main_Static --static

There are two kinds of links ：
Dynamic links ：GCC Default options at compile time . Dynamic means that the external code base is loaded only when the application is running , Different programs can share a code base . So the program generated by dynamic link is relatively small , Use less memory .
Static links ： Use options when linking “–static”, It will package all the libraries used in the compilation phase into its own executable program . So the advantage of static link is better compatibility , Independent of the external environment , But the generated program is relatively large .

Code optimization -O

-O0 -O1 -O2 -O3 Compiler optimization options 4 A level , -O0 No optimization ,-O3 The highest level of optimization .-O3 The optimization of will be more violent , But the optimization effect is very good

gcc main.c -O1 -o main

Directory of files required for compilation -I

When we were writing code , For the beauty of the whole project and the convenience of sorting the code , Generally, they will .c and .h Separate ,-I Directory name It can make gcc Find the file directory you want to link

gcc main.c -I ./inc -o main # contain inc All files in 

other

-g Generate debugging information . GNU The debugger can use this information
-lpthread If the file contains multiple threads
pkg-config opencv --libs contain opencv Of C++ library

---

Two 、Makefile file

If we input a long list of compiled instructions every time , It will be very troublesome , and makefile It can simplify our needs .
makefile A key grammar rule is as follows , Represents what goals you need to generate , What is the dependent part , Subsequent operations are placed in the command .

 The goal is ...:  rely on ...
     command 1
     command 2
    ...

Some special variables

[email protected]： The name of the target 

$^： Construct the required file list, and the names of all files 

$<： The name of the first file to construct the required file list 

$?： Construct the updated file in the required file list 

For specific knowledge, please refer to the following blog

https://blog.csdn.net/afei__/article/details/82696682
https://blog.csdn.net/BobYuan888/article/details/88640923

Let's start with a recent one Makefile file , You can also use it conveniently in the future . It contains c++ and c Part of the mixed compilation of languages

Makefile Example

BIN_DIR = bin
SRC_DIR = src
INC_DIR = inc
OBJ_DIR = obj

CC = gcc
C++ = g++
LD = gcc # Link the required compiler 
INC = -I$(INC_DIR)

CFLAGS += $(INC)
OPT = -O1
LDFLAGS = -lm

# C file 
OBJ_FILES_C = $(OBJ_DIR)/main.o \
			  $(OBJ_DIR)/jpeg.o \
			  $(OBJ_DIR)/show.o \
		    $(OBJ_DIR)/huff.o  
#  All the files 
OBJ_FILES = $(OBJ_FILES_C)
# Total link executable gcode The location of  
TARGET = $(BIN_DIR)/gcode
# all Represents the final generated file 
all: $(TARGET)

# c File compilation 
$(OBJ_DIR)/%.o: $(SRC_DIR)/%.c
	$(CC) $(CFLAGS) $(OPT) -c $< -o [email protected] 

# cpp File compilation 
$(OBJ_DIR)/%.o: $(SRC_DIR)/%.cpp
	$(C++) $(CFLAGS) $(OPT) -c $< -o [email protected] 

#  If you want to link to other libraries , Must be at the end of all .o When a file is linked as a file, it is linked opencv library  
#  If you are building .o When linking files, the library will eventually not be found 
$(TARGET) : $(OBJ_FILES_C)
	$(C++) $(LDFLAGS) $(OBJ_FILES_C) $(OPT) -o [email protected] -lpthread 
	# -lpthread Represents that the code contains multithreaded execution 
# $(C++) $(LDFLAGS) $(OBJ_FILES) -o [email protected] `pkg-config opencv --libs` # If included opencv Libraries need to be linked 
	@echo "> build success <"	

#make clean Instructions 
clean:
	rm -f $(TARGET) $(OBJ_FILES)

---

3、 ... and 、C and C++ Mixed programming

Post a blog

https://blog.csdn.net/this_is_me_anyway/article/details/79397018

Reference resources

gcc part
https://zhuanlan.zhihu.com/p/404682058
https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Overall-Options.html#Overall-Options
Makefile part
https://blog.csdn.net/BobYuan888/article/details/88640923
https://blog.csdn.net/afei__/article/details/82696682