Header file search rules when compiling with GCC

1, GCC search header file rules

1. First, gcc will look for the required header files from the current directory, usually user-defined header files.

2. gcc will search for header files according to the header file path specified by the -I parameter, as follows, the header file path is /usr/openwin/include, and /srv/lib is the dynamic library path.

   gcc -I /srv/include -L /srv/lib hello.c

3. gcc finds the required header files from its own environment variables C_INCLUDE_PATH, CPLUS_INCLUDE_PATH, OBJC_INCLUDE_PATH

4. Find the required header files from the default directory /usr/include /usr/local/include /usr/lib/gcc-lib/i386-li.
   If neither can be found, an error will be reported.

2. Specify the header file path in the makefile

#path to the compilerCC= /opt/gcc-linaro-7.4.1-2019.02-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-gcc#Specify the header file path, prompting warning compilation,CFLAGS=-Wall -I/home/develop/include#source file pathSRCS=main.c sum.c com.c#dynamic library pathLIBS=-L /usr/lib#Specify the target file, all .c files are renamed to .o files (retain the characters at %, and the rest of the characters should be replaced)OBJS=$(SRCS:%.c=%.o)#Specify the name of the executable fileEXECUTABLE=ssj_flyfish#Compile and generate object files$(EXECUTABLE):$(CC) -o $(EXECUTABLE) $(CFLAGS) $(SRCS) $(LIBS)