compiling for gdb using make

I am learning C++ in a Linux environment.
I have a simple program consisting of 3 files as follows;

carClassApp.cpp //contains main()
Car.cpp // class implementation file
Car.h // class header file

I am trying to compile it with a makefile as follows;

//////////////////////
car: Car.o carClassApp.o
g++ Car.o carClassApp.o –o car

Car.o: Car.cpp
g++ -c Car.cpp

carClassApp.o: carClassApp.cpp
g++ -c carClassApp.cpp
///////////////////

Does this look correct?

Now I want to compile it so I can use gdb to debug it.
Do I simply delete all *.o files then edit the makefile by replacing the two –c flags with –g flags and then run make again? i.e.

//////////////////////
car: Car.o carClassApp.o
g++ Car.o carClassApp.o –o car

Car.o: Car.cpp
g++ -g Car.cpp

carClassApp.o: carClassApp.cpp
g++ -g carClassApp.cpp
///////////////////

Not replace -c, just add "-g" to gcc. And while you are at it, perhaps you'd want to add "-Wall" to give you warnings, in case you do something the compiler can help you find.

--
Mats

Thanks. Should the -g flag be used in all stages of the compilation then? i.e.;

Code:

---

car: Car.o carClassApp.o
g++ Car.o carClassApp.o –o -g car

Car.o: Car.cpp
g++ -c -g Car.cpp

carClassApp.o: carClassApp.cpp
g++ -c -g carClassApp.cpp

---

Also, should Car.h be referenced specifically in the makefile? i.e.

Code:

---

car: Car.o carClassApp.o
g++ Car.o carClassApp.o –o -g car

Car.o: Car.cpp Car.h
g++ -c -g Car.cpp Car.h

carClassApp.o: carClassApp.cpp
g++ -c -g carClassApp.cpp

---

Car.cpp contains the line;

Code:

---

#include "Car.h"

---

Compiling and building has me a little confused all round. Does the position of the flags in the command matter?

Yes, for debug builds use -g for each file.

Also, you need to put a TAB at the beginning of each command line (i.e. the ones where you have "g++ ...". Must be a tab, not spaces.

I haven't tried your make script but...

First, if I remember correctly, indentation matters in a makefile.

Code:

---

carClassApp.o: carClassApp.cpp

g++ -c -g carClassApp.cpp

---

I don't know how much it should be indented but if you use an editor like emacs, you won't have to worry about how many spaces (or one tab) you need for proper indentation.

Also, I bet you'd need to fix:

Code:

---

g++ Car.o carClassApp.o –g -o car

---

The output option "-o" should always immediately precede the output file.

Also, the object file targets do have to be explicitly indicated

Code:

---

Car.o: Car.cpp Car.h

g++ -c -g Car.cpp Car.h -o Car.o

---

However, if you use automatic variables

Code:

---

Car.o: Car.cpp Car.h

g++ -c -g $^ -o $@

---

it becomes simpler. "$^" means replace this with everything in the dependency list and "$@" means replace this with the target.

You can even reduce the entire segment:

Code:

---

Car.o: Car.cpp Car.h
g++ -c -g Car.cpp Car.h

carClassApp.o: carClassApp.cpp
g++ -c -g carClassApp.cpp

---

with

Code:

---

%.o: %.cpp

g++ -c -g $< -o $@

---

However, for the above to work, you need another target which uses this target as a dependency. So the final version would work like

Code:

---

SRC = carClass.cpp Car.cpp
OBJ = ${SRC:%.cpp=%.o}

car: $(OBJ)

g++ -o $@ $^

%.o: %.cpp

g++ -c -g $< -o $@

---

Come to think of it, I don't think you have to specify output when compiling. The compiler will probably automatically convert "Cars.cpp" to "Cars.o" without you having to explicitly state it.

Thanks all. I will digest what you have said.
One thing I have found is that I tried;

Code:

---

car: Car.o carClassApp.o
          g++ Car.o carClassApp.o  -Wall –g -o car

---

And problems occurred. I found I had to use ;

Code:

---

car: Car.o carClassApp.o
          g++ Car.o carClassApp.o  -o car

---

Use of -Wall and -g caused problems when linking. Maybe they should only be used when compiling source code to create object files.

Quote:

---

Originally Posted by enuenu

Thanks all. I will digest what you have said.
One thing I have found is that I tried;

Code:

---

car: Car.o carClassApp.o
          g++ Car.o carClassApp.o  -Wall –g -o car

---

And problems occurred. I found I had to use ;

Code:

---

car: Car.o carClassApp.o
          g++ Car.o carClassApp.o  -o car

---

Use of -Wall and -g caused problems when linking. Maybe they should only be used when compiling source code to create object files.

---

You _NEED_ to use -g at the link stage, otherwise the compiler will not produce the debug symbols that gdb needs. You can still use gdb, but you won't get any source or detailed symbol information.

-Wall is only really useful in the compile stage [together with -c].

--
Mats