如何使用GDB调试operator.c文件？多文件C项目调试问题求助

Hey there! Let's work through why you can't debug operator.c and walk through exactly how to debug it with GDB.

The most common culprit here is missing debug symbols or incorrect compilation steps. Let's break down the key issues:

1. No debug symbols in operator.c: If you only added the -g flag when compiling main.c but not operator.c, GDB won't have the necessary info (like line numbers, variable mappings) to debug operator.c.
2. GDB can't find the source file: If you moved operator.c after compiling, GDB might not know where to look for the source code.

To debug any source file, you need to generate debug symbols for all your code. Here's the correct workflow:

Option 1: Compile step-by-step #

1. Compile main.c with debug symbols:

   gcc -g -c main.c -o main.o
   

2. Compile operator.c with debug symbols (this is the step you might have missed!):

   gcc -g -c operator.c -o operator.o
   

3. Link the object files into an executable:

   gcc main.o operator.o -o my_app
   

Option 2: Single-line compilation #

You can also compile all files in one go (just make sure -g is included):

gcc -g main.c operator.c -o my_app

If you use a Makefile #

Update your CFLAGS to include -g so debug symbols are added automatically:

CFLAGS = -g -Wall  # -Wall adds warnings, which is optional but helpful
my_app: main.o operator.o
    gcc $(CFLAGS) $^ -o $@
main.o: main.c header.h
operator.o: operator.c header.h

Once you have a properly compiled executable with debug symbols, here's how to debug operator.c:

1. Start GDB with your program #

gdb my_app

2. Set breakpoints in operator.c #

You have two easy ways to target operator.c:

• Break on a function: If you know the function name (e.g., calculate_sum), run:

  (gdb) break calculate_sum
  

• Break on a specific line: Use the format break filename:line_number:

  (gdb) break operator.c:22
  

  This will pause execution when the program hits line 22 of operator.c.

3. Run the program #

(gdb) run

The program will execute until it hits your breakpoint in operator.c.

4. Useful Debug Commands #

Once paused, use these commands to inspect and step through the code:

• step (or s): Step into the next line, including entering functions in operator.c
• next (or n): Step to the next line, skipping over function calls
• print <variable> (or p <variable>): Check the value of a variable in operator.c
• continue (or c): Resume execution until the next breakpoint
• backtrace (or bt): Show the current call stack (helpful if you hit an error)
• quit (or q): Exit GDB

5. Example Workflow #

Suppose operator.c has a function multiply that's behaving unexpectedly:

1. Set a breakpoint: (gdb) break multiply
2. Run the program: (gdb) run
3. When paused, check input values: (gdb) print a and (gdb) print b
4. Step through the function line by line: (gdb) s
5. Verify intermediate results with print to spot where things go wrong

If GDB says something like No source file named operator.c, tell it where to look:

• Use the directory command inside GDB:

  (gdb) directory /path/to/the/folder/containing/operator.c
  

• Or start GDB with the source directory upfront:

  gdb -d /path/to/source/folder my_app
  

内容的提问来源于stack exchange，提问作者shridhar