如何在子目录内使用.cpp和.h文件？

Question

This is the contents of a directory in my system:

/directory/
    classes/
        class1.cpp
        class1.h
    main.cpp

And here is the contents of above files:

main.cpp

   #include "classes/class1.h"

   int main(){
       class1 test;
       return 0;
   }

class1.h

   class class1 {
       public:
           class1();
           void test();
   };

class1.cpp

   #include "class1.h"

   class1::class1(){
   }
   class1::test(){
   }

The question is why I can't compile main.cpp ?

ghasemi@ghasemi-MS-7693:~/Desktop/directory$ g++ *.cpp
/tmp/ccEvIogL.o: In function `main':
main.cpp:(.text+0x1f): undefined reference to `class1::class1()'
collect2: error: ld returned 1 exit status

Answer 1

In your main directory there is only one .cpp file, and the * wildcard doesn't look in sub-directories. You need to explicitly name all the source files, or use multiple wildcards (not something I recommend).

So something like

g++ main.cpp classes/class1.cpp

Answer 2

What you are searching for is not related to the compiler (gcc) itself but to a build environment. There are several tools which do the job.

If you start with only a hand full of files, you can compile every file every time. But if your projects become bigger it is very time consuming to compile all files again and again, also if nothing has changed in some of them!

Most common for this job is gnu make.

You have to write a configuration which describes your project. This file is typically called "Makefile".

Here you define: Which files must be compiled if a file changes. Which files must be linked together. All parameters for linkage and compile for all or individual files. ... a lot more

So please take a look for https://www.gnu.org/software/make/manual/

For your project, it can be look like:

all: myprog

main.o: main.cpp classes/class1.h

classes/class1.o: classes/class1.cpp classes/class1.h

myprog: main.o classes/class1.o
    g++ main.o classes/class1.o -o myprog