Finding C++ Memory Leaks: Valgrind, AddressSanitizer,

Finding C++ Memory Leaks: Valgrind, AddressSanitizer,

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Finding C++ Memory Leaks: Valgrind, AddressSanitizer,

이 글의 핵심

Detect heap leaks with Valgrind memcheck, ASan+LSan, and Visual Studio CRT debug heap. Common leak patterns: new/delete mismatch, exceptions, shared_ptr cycles, containers of raw pointers.

Tooling: Valgrind · ownership in C++: smart pointers · Rust contrast: ownership.

Introduction: “Memory grows until OOM”

“The server runs for days, then dies”

A memory leak means you lose the last pointer to heap memory without freeing it. Long-running services eventually OOM.

// 실행 예제
void handle() {
    int* p = new int[1000];
    // forgot delete[]
}

This article covers:

  • Five major leak causes
  • Valgrind (Linux)
  • AddressSanitizer + LeakSanitizer
  • Visual Studio / CRT helpers
  • Ten leak patterns and RAII fixes
  • Production monitoring ideas

Table of contents

  1. What is a leak?
  2. Five major causes
  3. Valgrind
  4. AddressSanitizer
  5. Visual Studio heap
  6. Ten patterns
  7. RAII
  8. Production monitoring
  9. Summary

1. What is a memory leak?

Heap memory no longer reachable from any pointer in the program → cannot be freed → grows until limits. Contrast with intentional growth (e.g. a cache) where memory is still reachable.

2. Five major causes (overview)

  1. new/delete mismatch or missing delete
  2. Exception paths skipping manual cleanup
  3. shared_ptr cycles
  4. Containers of raw owning pointers without cleanup
  5. Singletons with raw new and no teardown

3. Valgrind

g++ -g -std=c++17 -o myapp main.cpp
valgrind --leak-check=full --show-leak-kinds=all ./myapp

Interpret definitely lost vs still reachable (globals may be “reachable” at exit).

4. AddressSanitizer / LeakSanitizer

g++ -g -fsanitize=address -std=c++17 -o myapp main.cpp
export ASAN_OPTIONS=detect_leaks=1
./myapp

Visual Studio: enable AddressSanitizer in project settings (version-dependent).

5. Visual Studio / CRT

_CrtSetDbgFlag with _CRTDBG_LEAK_CHECK_DF in debug builds for leak dumps on exit.

6. Ten patterns (titles)

  1. Raw new without delete
  2. Exception before delete → RAII
  3. new[] paired with wrong delete
  4. vector<T*> without deleting elements
  5. shared_ptr cycle → weak_ptr
  6. Conditional delete paths
  7. Rule-of-five violations (double free / leak)
  8. Factory returning raw owning pointer without documented ownership
  9. Globals with manual new
  10. Thread stacks leaking thread-local new

7. RAII

Acquire in constructor / release in destructor — unique_ptr, vector, file handles, locks.

8. Production monitoring

/proc/self/status VmRSS on Linux, custom allocation counters (carefully—global operator new hooks affect everything), periodic sanity checks against baselines.

Summary

Tool comparison

ToolPlatformSpeedRebuild
ValgrindLinuxSlowNo
ASan/LSanMany~2×Yes
VS heapWindowsFastDebug helpers

Rules

  1. Prefer make_unique / make_shared over raw new.
  2. Containers should usually own values or smart pointers, not raw pointers.
  3. Break shared_ptr cycles with weak_ptr.
  4. Run ASan/Valgrind in CI on tests.

Keywords

memory leak, Valgrind, AddressSanitizer, LeakSanitizer, RAII, new delete

Practical tips

  • Enable ASan on developer builds by default.
  • Add Valgrind stage for release candidates on Linux.
  • Review any returning raw owning pointer APIs.

Closing

Leaks are common but preventable: RAII, smart pointers, no cycles, and automated leak checks in CI. Next: Use-after-free and deeper Valgrind articles.

Frequently Asked Questions (FAQ)

Q. When would I use this in practice?

A. Detect heap leaks with Valgrind memcheck, ASan+LSan, and Visual Studio CRT debug heap.

Q. What should I read before this?

A. Follow the previous article or related articles links at the bottom of each post to learn in sequence. See the C++ series index for the full picture.

Q. Where can I study this more deeply?

A. Check cppreference and the relevant library’s official documentation. The reference links at the end of the article are also worth using.

Other articles related to this topic.

Keywords Covered in This Article (Related Search Terms)

This article covers C++, Memory leak, Valgrind, AddressSanitizer, LeakSanitizer, RAII, Debugging.