Online GDB Compiler

What Is an Online GDB Compiler?

GDB, the GNU Debugger, is the standard debugger for C and C++ programs on Linux. People often search for an online GDB compiler when they want to test C or C++ code without installing a toolchain.

This tool compiles and runs your code with GCC in a sandbox, and shows the output, compiler errors and any crash signal. It doesn't include an interactive GDB session, so you can't set breakpoints or step through code here. For that, install GDB on your own computer and use the commands listed in this article.

How to Use It

1. The editor opens with a C sample. Use the language menu to switch to C++ or another language.
2. Write or paste your program.
3. If your program reads input, add it to the Standard Input panel before you run it. The program can't stop and wait for you to type.
4. Select Run code, or press Ctrl+Enter (Cmd+Enter on a Mac).

Reading the Result

Debugging Without GDB

Without breakpoints, print statements are the quickest way to find where a program goes wrong. Output is often held in a buffer and can be lost in a crash, so write it out straight away:

#include <stdio.h>

int main(void) {
    /* Write all output immediately, so a crash can't discard it */
    setvbuf(stdout, NULL, _IONBF, 0);

    printf("Before the suspect line\n");
    /* ... */
    printf("After the suspect line\n");
    return 0;
}

The last message you see shows that the problem comes after that line. Move the messages closer together until you find it.

Debugging With GDB on Your Computer

To use GDB itself, compile with debug information and without optimization, then start the program in GDB:

gcc -g -O0 main.c -o main
gdb ./main

For C++, use g++ in place of gcc. These commands cover most debugging sessions:

To find memory errors, also try compiling with -fsanitize=address. The program then reports invalid memory access with the location of the problem.

Limits

Programs run from a single file, so you can't add your own headers or libraries.

For the full list of languages, see the Online Compiler. It uses the same engine and opens on Python.