GCC and makefile

Preface

Self contact C Since the language , Small demo direct gcc, Of large projects Makefile They are all built-in in the framework , It's usually repaired as needed , The specific rules are always confused ！ When you build a small project , Rub one of your hands Makefile It's really hard. , I can't write it at all , So book this blog , Later ctrl+c.
This article will not expand on how to write a Makefile. For details , Please refer to the following very detailed tutorial , Contains almost GNU make Of Makefile All the details of ：

Write with me Makefile

This article contains the following ：

• makefile Small template
• gcc Instructions

Makefile Small template

For pure Ｃ Language

#  Instruction compiler and options 
CC=gcc
CFLAGS=-Wall -std=gnu99
 
#  Target file 
TARGET=main
SRCS = main1.c \
   			main2.c  \
   			main3.c  
INC = -I./
OBJS = $(SRCS:.c=.o)

$(TARGET):$(OBJS)
	$(CC) -o [email protected] $^
 
clean:
	rm -rf $(TARGET) $(OBJS)
 
%.o:%.c
	$(CC) $(CFLAGS) $(INC) -o [email protected] -c $<

Be careful ：Makefile There is a rule that the command line is based on tab Key start ,4 Spaces or others will report errors ：
Makefile:2: *** missing separator.stop

• Compared to a single file and multiple files makefile, Through the variable INC The header file path is established . Header file paths are separated by spaces .
• Compilation Rules %.o:%.c Header file parameters are added to $(CC) $(CFLAGS) $(INC) -o [email protected] -c $<,
• Single file and multiple files makefile The header file path parameter is added .
• SRCS variable , If there are many documents, you can use “\” Symbol continuation .
• [email protected] -- Represents the target document
• $^ -- Represents all dependent files
• $< -- Represents the first dependent file ( The one on the far left ).

Apply to C/C++ Mixed compilation

The directory structure is as follows ：

httpserver
│   main.cpp
│   Makefile  
└─────inc
│      │   mongoose.h
│      │   http_server.h
│   
──────src
│       │   http_server.cpp
│       │   mongoose.c
│       │   ...

Makefile as follows ：

CC=gcc
CXX=g++

#  Compiler parameter settings at compile time , Include header file path settings 
CFLAGS:=-Wall -O2 -g 
CFLAGS+=-I $(shell pwd)/inc
CXXFLAGS:=-Wall -O2 -g -std=c++11
CXXFLAGS+=-I $(shell pwd)/inc

#  Library file add 
LDFLAGS:=
LDFLAGS+=

#  Specify the storage location of the source program 
SRCDIRS:=.
SRCDIRS+=src

#  Set the file type used in the program 
SRCEXTS:=.c .cpp

#  Set the name of the running program 
PROGRAM:=httpserver

SOURCES=$(foreach d,$(SRCDIRS),$(wildcard $(addprefix $(d)/*,$(SRCEXTS))))
OBJS=$(foreach x,$(SRCEXTS),$(patsubst %$(x),%.o,$(filter %$(x),$(SOURCES))))

.PHONY: all clean distclean install

%.o: %.c
	$(CC) -c $(CFLAGS) -o [email protected] $<
	
%.o: %.cxx
	$(CXX) -c $(CXXFLAGS) -o [email protected] $<


$(PROGRAM): $(OBJS)
ifeq ($(strip $(SRCEXTS)),.c)
	$(CC) -o $(PROGRAM) $(OBJS) $(LDFLAGS)
else
	$(CXX) -o $(PROGRAM) $(OBJS) $(LDFLAGS)
endif


install:
	install -m 755 -D -p $(PROGRAM) ./bin

clean:
	rm -f $(shell find -name "*.o")
	rm -f $(PROGRAM)

distclean:
	rm -f $(shell find -name "*.o")
	rm -f $(shell find -name "*.d")
	rm -f $(PROGRAM)

all:
	@echo $(OBJS)

gcc Instructions

One step in place

gcc main.c -o main

Compilation of multiple program files

gcc main1.c main2.c -o main

Preprocessing

gcc -E main.c -o main.i
or
gcc -E main.c
gcc Of -E Options , You can make the compiler stop after preprocessing , And output the preprocessing results .

Compile into assembly code

After pretreatment , Can be generated directly on test.i File compilation , Generate assembly code :
gcc -S main.i -o main.s
gcc Of -S Options , Indicates that during program compilation , After generating assembly code , stop it ,-o Output assembly code file .

assembly

For the assembly code file generated above test.s,gas The assembler is responsible for compiling it into the target file , as follows :
gcc -c main.s -o main.o

Connect

gcc The connector is gas Provided , Be responsible for connecting the object file of the program with all additional object files required , Final generation of executable . Additional target files include static connection library and dynamic connection Library .
For the... Generated in the previous section main.o, With the Ｃ Connect to standard I / O libraries , Finally generate executable program main.

Error detection

Parameters -Wall, Use it to make GCC Generate as many warning messages as possible .
gcc -Wall main.c -o main
Bring... When compiling the program -Werror Options , that GCC Will stop compiling wherever warnings are generated , Force programmers to modify their code , as follows ：
gcc -Werrormain.c -o main

Create a dynamic link library

To generate o file
gcc -c -fPIC add.c // We have to add -fPIC Options , The purpose is to make the library not care about the function location in the file
To compile
gcc -shared -fPIC -o libadd.so add.o

Library file connection

When developing software , It's rare not to use a third-party library at all , Generally speaking, we need the support of many function libraries to complete the corresponding functions . From a programmer's point of view , The function library is actually some header files （.h） And libraries （so、 or lib、dll） Set . although Linux Most of the functions under will put the header file in by default /usr/include/ Under the table of contents , The library file is placed in /usr/lib/ Under the table of contents ; But sometimes , The library we want to use is not in these directories , therefore GCC When compiling, you must use your own method to find the required header file and library file .
Add extra ：Linux Connection required so The library files （ With soft connection ）, It can be completely copied to /usr/include/ or /usr/lib/ Under the table of contents , Use cp -d * /usr/lib/ command , Then don't forget to run again ldconfig.

among inclulde The path to the folder is /home/test/include,lib The folder is /home/test/lib,lib The folder contains binary so file libtest.so
First, compile main.c For the target file , This is the time to execute :
gcc –c –I /home/test/include main.c –o main.o
Finally, link all the target files into executable files :
gcc –L /home/test/lib -ltest main.o –o main

By default , GCC Dynamic link library is preferred when linking , Consider using static link libraries only if they don't exist , Add... At compile time if necessary -static Options , Force the use of static link libraries .
gcc –L /home/test/lib -static -ltest main.o –o main

Search path order when static library Links ：

1. ld Will go to GCC Parameters in the command -L
2. Look again gcc Environment variables of LIBRARY_PATH
3. Find the internal directory again /lib、 /usr/lib、 /usr/local/lib This is when compile gcc It's written in the program

Dynamic links 、 Search path order at execution time :

1. The dynamic library search path specified when compiling the object code
2. environment variable LD_LIBRARY_PATH Specified dynamic library search path
3. The configuration file /etc/ld.so.conf The dynamic library search path specified in
4. Default dynamic library search path /lib
5. Default dynamic library search path /usr/lib

Related environment variables ：
LIBRARY_PATH environment variable ： Specify the program static link library file search path
LD_LIBRARY_PATH environment variable ： Specify the program DLL file search path