VSCode C Tutorial

Simple beginner's guide to using the Visual Studio Code C/C++ debugger and an address sanitizer in Linux. Everything mentioned works for C++ as well, just change gcc/clang to g++/clang++ wherever necessary and use your C++ source files.

Debugger

Open this folder with VSCode (File -> Open Folder -> ...)
Make sure you have the C/C++ Extension Pack installed.
Install the necessary tools.

If you are on a Debian-based distro:
```
sudo apt install build-essentials
```
If you are on a Arch-based distro:
```
sudo pacman -S base-devel
```
If you are on a RHEL based distro:
```
sudo dnf install "@Development Tools"
```

Create a source file with the following contents. We will use this file to test the debugger and address sanitizer.

// main.c
#include <stdio.h>
#include <string.h>

int main(int argc, char** argv)
{
if (argc >= 2)
{
    printf("Hello, %s\n", argv[1]);
    return 0;
}

// Force a segfault
memset(NULL, 32, 32); // Boom!

return 0;
}

Write a basic Makefile

# Makefile

main: main.c
    gcc -g3 -Og -Wall -pedantic -o main main.c

Create a folder called .vscode at the root of the project space.

Create a file .vscode/launch.json with the following contents:

{
  // Use IntelliSense to learn about possible attributes.
  // Hover to view descriptions of existing attributes.
  // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
  "version": "0.2.0",
  "configurations": [
    {
      "name": "(gdb) Launch",
      "type": "cppdbg",
      "request": "launch",
      "program": "${workspaceFolder}/main",
      "args": [],
      "stopAtEntry": false,
      "cwd": "${workspaceFolder}",
      "environment": [],
      "externalConsole": false,
      "MIMode": "gdb",
      "setupCommands": [
        {
          "description": "Enable pretty-printing for gdb",
          "text": "-enable-pretty-printing",
          "ignoreFailures": true
        },
        {
          "description": "Set Disassembly Flavor to Intel",
          "text": "-gdb-set disassembly-flavor intel",
          "ignoreFailures": true
        }
      ]
    }
  ]
}

You can customize this to target any executable name by editing the program item. You can also add CLI arguments by editing the args list. This is equivalent to passing each item separated by a space on the commad line. Give it a try.

Navigate to a terminal and compile your program.
```
make
```
Start the debugger by pressing F5 in VSCode. The debugger will automatically break at the location of the segmentation fault.

Address Sanitizer

Alternatively, you can use an address sanitizer to catch memory leaks, and invalid memory accesses.

Using an address sanitizer with the VScode debugger usually will not work. To switch between the two, disable the address sanitizer and recompile before trying to use the debugger.

Create a C file with the following contents.

// main.c
#include <stdio.h>
#include <string.h>

int main(int argc, char** argv)
{
if (argc >= 2)
{
    printf("Hello, %s\n", argv[1]);
    return 0;
}

// Force a segfault
memset(NULL, 32, 32); // Boom!

return 0;
}

Write a slightly more complex Makefile with a target for with and without the address sanitizer.

# Makefile

.PHONY: main debug

all: main

main: main.c
    gcc -g3 -Og -Wall -pedantic -o main main.c

debug: main.c
    gcc -g3 -Og -Wall -pedantic -fsanitize=address,undefined,leak -o main main.c

Notice the addition of the -fsanitize=address,undefined,leak flag.

Compile and run. The new Makefile adds a second debug target which compiles with the address sanitizer.

$ make

$ ./main
  [1]    11272 segmentation fault (core dumped)  ./main

$ make debug

$ ./main
  main.c:14:3: runtime error: null pointer passed as argument 1, which is declared to neverbe null
  AddressSanitizer:DEADLYSIGNAL
  =================================================================
  ==11571==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7fae35f7d259 bp 0x000000000001 sp 0x7ffc4da6f928 T0)
  ==11571==The signal is caused by a WRITE memory access.
  ==11571==Hint: address points to the zero page.
      #0 0x7fae35f7d259  (/usr/lib/libc.so.6+0x167259) (BuildId: 2f005a79cd1a8e385972f5a102f16adba414d75e)
      #1 0x5593b702e25b in main /home/joshua/repos/vscode-c-tutorial/main.c:14
      #2 0x7fae35e3984f  (/usr/lib/libc.so.6+0x2384f) (BuildId: 2f005a79cd1a8e385972f5a102f16adba414d75e)
      #3 0x7fae35e39909 in __libc_start_main (/usr/lib/libc.so.6+0x23909) (BuildId: 2f005a79cd1a8e385972f5a102f16adba414d75e)
      #4 0x5593b702e0f4 in _start (/home/joshua/repos/vscode-c-tutorial/main+0x10f4) (BuildId: 9a808a76b2632b10eb243ccfa68ed3f2ffa39e05)

  AddressSanitizer can not provide additional info.
  SUMMARY: AddressSanitizer: SEGV (/usr/lib/libc.so.6+0x167259) (BuildId: 2f005a79cd1a8e385972f5a102f16adba414d75e)
  ==11571==ABORTING

Within this output you can see the file and line number the error occurred and a description of what has gone wrong, in this case a SEGV (segmentation fault) on unknown adress 0x00.. aka the NULL pointer ((void)0).

jarulsamy / vscode-c-tutorial

VSCode C Tutorial

Debugger

Address Sanitizer

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