msvc-cl

Q: How do I install msvc-cl?

Run npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill msvc-cl in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/msvc-cl/ (personal) or .claude/skills/msvc-cl/ (project).

by mohitmishra786

MSVC cl.exe and clang-cl skill for Windows C/C++ projects. Use when configuring Visual Studio builds, MSBuild, or clang-cl as a drop-in MSVC replacement. Covers translating GCC/Clang flags to MSVC equivalents, runtime library selection, Windows SDK setup, and diagnosing MSVC-specific errors. Activates on queries about cl.exe, clang-cl, /O flags, /MT vs /MD, PDB files, Windows ABI, or MSVC project settings.

Installs: 620
Last 24h: —
Trending rank: —
Security: Not audited

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill msvc-cl

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads msvc-cl automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

MSVC cl.exe and clang-cl

Purpose

Guide agents through Windows C/C++ compilation: MSVC cl.exe, clang-cl as MSVC-compatible driver, MSBuild project settings, and runtime library choices.

Triggers

"How do I compile with MSVC from the command line?"
"What is the MSVC equivalent of -O2?"
"/MT vs /MD — which do I use?"
"How do I use clang-cl instead of cl.exe?"
"I'm getting LNK errors on Windows"
"How do I generate PDB files?"

Workflow

1. Set up the environment

MSVC requires the Visual Studio environment variables. Use the Developer Command Prompt or set up manually:

REM x64 native
"C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvars64.bat"

REM x86 cross (host x64, target x86)
"...\vcvarsamd64_x86.bat"

REM Check compiler version
cl /?

In CMake, use the "Visual Studio 17 2022" generator or pass -DCMAKE_GENERATOR="Visual Studio 17 2022".

2. Flag translation: GCC → MSVC

GCC/Clang	MSVC cl.exe	Notes
`-O0`	`/Od`	Debug, no optimisation
`-O1`	`/O1`	Minimise size
`-O2`	`/O2`	Maximise speed
`-O3`	`/Ox`	Full optimisation
`-Os`	`/Os`	Favour size
`-g`	`/Zi`	PDB debug info
`-g` (embedded)	`/Z7`	Debug info in object file
`-Wall`	`/W3` or `/W4`	Warning level
`-Werror`	`/WX`	Warnings as errors
`-std=c++17`	`/std:c++17`	Standard selection
`-DFOO=1`	`/DFOO=1`	Preprocessor define
`-I path`	`/I path`	Include path
`-c`	`/c`	Compile only (no link)
`-o out`	`/Fe:out.exe` or `/Fo:out.obj`	Output file
`-shared`	`/LD`	Build DLL
`-fPIC`	(implicit on Windows)	Not needed on Windows
`-flto`	`/GL` (compile) + `/LTCG` (link)	Whole program optimisation

3. Runtime library selection

This is the most common source of LNK errors on Windows.

Flag	Runtime	Use case
`/MD`	`MSVCRT.dll` (dynamic)	Release, DLL linkage (recommended default)
`/MDd`	`MSVCRTd.dll` (debug dynamic)	Debug builds
`/MT`	Static CRT	Standalone exe; avoid mixing with DLLs
`/MTd`	Static CRT debug	Debug + static

Rule: All objects and libraries in a link must use the same runtime. Mixing /MT and /MD causes LNK2038: mismatch detected.

4. clang-cl

clang-cl is Clang's MSVC-compatible driver. It accepts cl.exe-style flags and can replace cl.exe in most MSBuild/CMake projects.

REM Install: part of LLVM Windows release or VS "LLVM" component

REM Basic usage (MSVC-style flags)
clang-cl /O2 /std:c++17 /MD src.cpp /Fe:prog.exe

REM Pass Clang-native flags with /clang:
clang-cl /O2 /clang:-Rpass=inline src.cpp /Fe:prog.exe

REM Use in CMake
cmake -DCMAKE_C_COMPILER=clang-cl -DCMAKE_CXX_COMPILER=clang-cl ..

Minimum Clang version for MSVC STL compatibility: Clang 8+. For C++20 features with MSVC STL: Clang 14+.

Source: https://learn.microsoft.com/en-us/cpp/build/clang-support-msbuild

5. PDB files and debugging

REM Compile with /Zi (external PDB) and /Fd (PDB name)
cl /Zi /Fd:prog.pdb /O2 src.cpp /link /DEBUG

REM /Z7: debug info embedded in .obj (no separate PDB for objects)
cl /Z7 /O2 src.cpp /link /DEBUG /PDB:prog.pdb

For WinDbg or VS debugger, ensure the PDB is alongside the executable or set the symbol path.

6. Common LNK errors

Error	Cause	Fix
`LNK2019: unresolved external`	Missing `.lib`	Add library in project settings or `/link foo.lib`
`LNK2038: mismatch detected for 'RuntimeLibrary'`	Mixed `/MT` and `/MD`	Unify all to `/MD` or `/MT`
`LNK1104: cannot open file 'foo.lib'`	Library not in search path	Add path via `/LIBPATH:` or `LIB` env var
`LNK2005: already defined`	Multiple definitions	Use `__declspec(selectany)` or check for duplicate definitions
`LNK4098: defaultlib 'LIBCMT' conflicts`	Runtime mismatch	Explicitly pass `/NODEFAULTLIB:LIBCMT` or unify runtimes

7. Useful cl.exe flags

REM Preprocessed output
cl /P src.cpp       # produces src.i

REM Assembly output
cl /FA /O2 src.cpp  # produces src.asm (MASM syntax)
cl /FAs             # interleave source + asm

REM Show include files
cl /showIncludes src.cpp

REM Compiler version
cl /?  2>&1 | findstr /i "version"

For flag details, see references/flags.md.

Related skills

Use skills/compilers/clang for clang-cl's Clang-native diagnostics
Use skills/build-systems/cmake for CMake toolchain configuration on Windows
Use skills/debuggers/lldb or WinDbg for debugging MSVC-built binaries

FAQ

What does the msvc-cl skill do?

How do I install msvc-cl?

Run npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill msvc-cl in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/msvc-cl/ (personal) or .claude/skills/msvc-cl/ (project).

Which AI agents can use msvc-cl?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is msvc-cl safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains msvc-cl?

It is published by mohitmishra786 in mohitmishra786/low-level-dev-skills. It has 620 recorded installs.