How to use gdb in Ubuntu Terminal

Here's a practical, minimal guide for using GDB in Ubuntu terminal — from launching to setting breakpoints and navigating your code.

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🧰 Step 1: Compile with Debug Symbols

Use -g and disable optimizations (-O0 preferred for debugging):

bash
g++ -g -O0 -o myprog myprog.cpp

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🚀 Step 2: Launch GDB

bash
gdb ./myprog

You'll see a (gdb) prompt.

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🎯 Step 3: Set Breakpoints

You can set breakpoints in three main ways:

✅ a. At a function

gdb
(gdb) break main

✅ b. At a specific file and line

gdb
(gdb) break myprog.cpp:42

✅ c. At a method in a class

gdb
(gdb) break MyClass::doSomething

If the symbol is mangled (C++), GDB usually demangles automatically, especially if compiled with -g.

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▶️ Step 4: Run the Program

gdb
(gdb) run

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🧭 Step 5: Navigate

Command	Meaning
next or n	Step over current line
step or s	Step into function call
finish	Run until current function returns
continue or c	Continue until next breakpoint
list	Show source code around current line
info locals	Show all local variables
print x	Print variable x

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⛏️ Step 6: Manage Breakpoints

List breakpoints:

gdb
(gdb) info breakpoints

Delete a breakpoint:

gdb
(gdb) delete <number>

Disable/Enable breakpoint temporarily:

gdb
(gdb) disable <number>
(gdb) enable <number>

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🧪 Example Session

bash
g++ -g -O0 -o test test.cpp
gdb ./test

gdb
(gdb) break main
(gdb) break test.cpp:18
(gdb) run
(gdb) next
(gdb) print myVar
(gdb) continue

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🧠 Pro Tips

• Press <TAB> for autocompletion.

• Use layout src in GDB to get a TUI (text UI).

• quit to exit.

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🪟 Bonus: GDB Text UI Mode

In GDB:

gdb
(gdb) layout src

→ Shows source code window with current line highlighted. Use arrow keys or n, s, etc.

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Let me know if you'd like:

• Watchpoints (for memory change)

• Debugging core dumps

• Pretty printing with gdbinit

• Automating GDB session with scripts