c-cpp-compilers

Compare original and translation side by side

🇺🇸

Original

English

🇨🇳

Translation

Chinese

C/C++ Compilers

C/C++ 编译器

Guidance for compiling, analyzing, and optimizing C and C++ code with GCC and Clang in 2026.

2026年使用GCC和Clang编译、分析及优化C和C++代码的指南。

Reference files

参考文档

GCC specifics: gcc.md -- flags, diagnostics, PGO, LTO, error triage
Clang specifics: clang.md -- diagnostics, optimization remarks, clang-tidy, macOS
Sanitizers: sanitizers.md -- ASan, UBSan, TSan, MSan, LSan decision tree and reports
Static analysis: static-analysis.md -- clang-tidy, cppcheck, scan-build, CI integration
Modern C/C++: modern-cpp.md -- C++20 modules, C++23/26 features, C23, migration

GCC 专属内容：gcc.md -- 标志、诊断信息、PGO、LTO、错误排查
Clang 专属内容：clang.md -- 诊断信息、优化备注、clang-tidy、macOS 适配
Sanitizer：sanitizers.md -- ASan、UBSan、TSan、MSan、LSan 决策树及报告解读
静态分析：static-analysis.md -- clang-tidy、cppcheck、scan-build、CI 集成
现代C/C++：modern-cpp.md -- C++20 模块、C++23/26 特性、C23、版本迁移

Standards baseline (2026)

标准基线（2026）

Language	Preferred standard	GCC support	Clang support
C	`-std=c23` (or `-std=c17` for broad compat)	GCC 15+	Clang 18+
C++	`-std=c++23` (or `-std=c++20` minimum)	GCC 14+	Clang 18+

Always pass the standard flag explicitly. Never rely on compiler defaults.

语言	推荐标准	GCC支持版本	Clang支持版本
C	`-std=c23` （兼容广泛场景使用 `-std=c17` ）	GCC 15+	Clang 18+
C++	`-std=c++23` （最低要求 `-std=c++20` ）	GCC 14+	Clang 18+

始终显式传递标准标志，切勿依赖编译器默认值。

Build modes

构建模式

Goal	Flags
Debug	`-g -O0 -Wall -Wextra -Wpedantic`
Debug (GDB-friendly optimized)	`-g -Og -Wall -Wextra`
Release	`-O2 -DNDEBUG -Wall`
Release (max throughput, native)	`-O3 -march=native -DNDEBUG -flto`
Release (min binary size)	`-Os -DNDEBUG` (Clang: `-Oz` )
Sanitizer build	`-g -O1 -fsanitize=address,undefined -fno-omit-frame-pointer`

目标	标志
调试	`-g -O0 -Wall -Wextra -Wpedantic`
调试（GDB友好的优化版本）	`-g -Og -Wall -Wextra`
发布	`-O2 -DNDEBUG -Wall`
发布（最大吞吐量，原生适配）	`-O3 -march=native -DNDEBUG -flto`
发布（最小二进制体积）	`-Os -DNDEBUG` （Clang： `-Oz` ）
Sanitizer 构建	`-g -O1 -fsanitize=address,undefined -fno-omit-frame-pointer`

Warning discipline

警告规范

Start with

-Wall -Wextra -Wpedantic

. Add

-Werror

in CI.

Suppress narrow scopes only:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
void callback(int ctx, int unused) { (void)ctx; }
#pragma GCC diagnostic pop

Clang equivalent works the same. For project-wide suppression, prefer

.clang-tidy

config or

-Wno-<flag>

in build system, not in source.

从

-Wall -Wextra -Wpedantic

开始，在CI环境中添加

-Werror

。

仅在窄范围内抑制警告：

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
void callback(int ctx, int unused) { (void)ctx; }
#pragma GCC diagnostic pop

Clang 等效语法作用相同。如需项目级别的警告抑制，优先使用

.clang-tidy

配置或构建系统中的

-Wno-<flag>

，而非在源码中处理。

Optimization decision tree

优化决策树

Need max throughput on known hardware?
  yes -> -O3 -march=native -flto
  no  -> Have profiling data?
           yes -> -O2 -fprofile-use (GCC) / -fprofile-instr-use (Clang)
           no  -> -O2

Size-constrained (embedded, shared lib)?
  yes -> -Os (GCC/Clang) or -Oz (Clang only)

Numerical code that tolerates IEEE relaxation?
  yes -> -Ofast (enables -ffast-math; breaks NaN/inf handling)
  no  -> stay with -O2/-O3

-O3

-O2

-O3

adds aggressive loop transforms and wider inlining. Benchmark before committing -- i-cache pressure can cause regressions.

是否需要在已知硬件上达到最大吞吐量？
  是 -> -O3 -march=native -flto
  否 -> 是否有性能分析数据？
           是 -> -O2 -fprofile-use (GCC) / -fprofile-instr-use (Clang)
           否 -> -O2

是否受体积限制（嵌入式、共享库）？
  是 -> -Os (GCC/Clang) 或 -Oz (仅Clang)

数值计算代码是否允许放宽IEEE标准？
  是 -> -Ofast（启用-ffast-math；会破坏NaN/inf处理）
  否 -> 保持使用-O2/-O3

-O3

-O2

：

-O3

增加了激进的循环转换和更广泛的内联。在提交前务必进行基准测试——指令缓存压力可能导致性能退化。

LTO

bash

undefined

bash

undefined

GCC

gcc -O2 -flto=auto -c foo.c bar.c gcc -O2 -flto=auto foo.o bar.o -o prog

Clang (ThinLTO preferred for large projects)

Clang（大型项目优先使用ThinLTO）

clang -O2 -flto=thin -fuse-ld=lld -c foo.c bar.c clang -O2 -flto=thin -fuse-ld=lld foo.o bar.o -o prog


Use `gcc-ar` / `gcc-ranlib` for GCC LTO archives. Clang ThinLTO links 5-10x faster than full LTO with comparable code quality.

clang -O2 -flto=thin -fuse-ld=lld -c foo.c bar.c clang -O2 -flto=thin -fuse-ld=lld foo.o bar.o -o prog


GCC LTO 归档需使用 `gcc-ar` / `gcc-ranlib`。Clang ThinLTO 的链接速度比全量LTO快5-10倍，且代码质量相当。

PGO (profile-guided optimization)

PGO（基于性能分析的优化）

GCC:

bash

gcc -O2 -fprofile-generate prog.c -o prog_inst
./prog_inst < workload.input
gcc -O2 -fprofile-use -fprofile-correction prog.c -o prog

Clang (LLVM instrumentation):

bash

clang -O2 -fprofile-instr-generate prog.c -o prog_inst
./prog_inst < workload.input
llvm-profdata merge -output=prog.profdata default.profraw
clang -O2 -fprofile-instr-use=prog.profdata prog.c -o prog

GCC：

bash

gcc -O2 -fprofile-generate prog.c -o prog_inst
./prog_inst < workload.input
gcc -O2 -fprofile-use -fprofile-correction prog.c -o prog

Clang（LLVM 插桩）：

bash

clang -O2 -fprofile-instr-generate prog.c -o prog_inst
./prog_inst < workload.input
llvm-profdata merge -output=prog.profdata default.profraw
clang -O2 -fprofile-instr-use=prog.profdata prog.c -o prog

Sanitizer quick reference

Sanitizer 速查

Bug class	Sanitizer	Flag
Heap/stack/global OOB, use-after-free, double-free	ASan	`-fsanitize=address`
Signed overflow, null deref, bad shift, misaligned access	UBSan	`-fsanitize=undefined`
Data races	TSan	`-fsanitize=thread`
Uninitialised reads (Clang only, all-instrumented build)	MSan	`-fsanitize=memory`
Memory leaks	LSan	via ASan ( `detect_leaks=1` ) or standalone

Common combo:

-fsanitize=address,undefined -fno-sanitize-recover=all -fno-omit-frame-pointer -g -O1

TSan and MSan are mutually exclusive with ASan. See sanitizers.md for report interpretation.

缺陷类型	Sanitizer	标志
堆/栈/全局内存越界、释放后使用、重复释放	ASan	`-fsanitize=address`
有符号溢出、空指针解引用、非法移位、未对齐访问	UBSan	`-fsanitize=undefined`
数据竞争	TSan	`-fsanitize=thread`
未初始化读取（仅Clang支持，需全插桩构建）	MSan	`-fsanitize=memory`
内存泄漏	LSan	通过ASan启用（ `detect_leaks=1` ）或独立使用

常用组合：

-fsanitize=address,undefined -fno-sanitize-recover=all -fno-omit-frame-pointer -g -O1

TSan 和 MSan 与 ASan 互斥。报告解读请参考 sanitizers.md。

Static analysis (quick start)

静态分析（快速入门）

bash

undefined

bash

undefined

Generate compilation database

生成编译数据库

cmake -S . -B build -DCMAKE_EXPORT_COMPILE_COMMANDS=ON

Run clang-tidy (recommended checks)

运行clang-tidy（推荐检查项）

clang-tidy -checks='bugprone-,clang-analyzer-,performance-,modernize-'
-p build src/foo.cpp

Run cppcheck

运行cppcheck

cppcheck --enable=warning,performance,portability --error-exitcode=1 src/


See [static-analysis.md](reference/static-analysis.md) for `.clang-tidy` config, CI integration, and suppression patterns.

cppcheck --enable=warning,performance,portability --error-exitcode=1 src/


`.clang-tidy` 配置、CI集成及警告抑制模式请参考 [static-analysis.md](reference/static-analysis.md)。

Common error triage

常见错误排查

Symptom	Likely cause	Fix
`undefined reference to 'foo'`	Missing `-lfoo` or wrong link order	Libraries after objects: `gcc main.o -lfoo`
`multiple definition of 'x'`	Defined in header without `static` / `inline`	`extern` in header, define in one `.c`
`implicit declaration of function`	Missing `#include` or wrong standard	Add the header; check `-std=`
`incompatible pointer types`	Wrong cast or missing prototype	Fix type; enable `-Wall`
ABI errors in C++	Mixed `-std=` or different `libstdc++`	Unify standard across all TUs
`relocation truncated`	32-bit relocation overflow	`-mcmodel=large` or restructure

症状	可能原因	修复方案
`undefined reference to 'foo'`	缺少 `-lfoo` 或链接顺序错误	库放在目标文件之后： `gcc main.o -lfoo`
`multiple definition of 'x'`	在头文件中定义变量但未加 `static` / `inline`	头文件中用 `extern` 声明，在单个 `.c` 文件中定义
`implicit declaration of function`	缺少 `#include` 或标准版本错误	添加对应头文件；检查 `-std=` 标志
`incompatible pointer types`	类型转换错误或缺少函数原型	修正类型；启用 `-Wall`
C++ 中的ABI错误	混合使用不同 `-std=` 标准或 `libstdc++` 版本	统一所有编译单元的标准版本
`relocation truncated`	32位重定位溢出	使用 `-mcmodel=large` 或重构代码

CMake integration

CMake 集成

cmake

cmake_minimum_required(VERSION 3.28)
project(myproject LANGUAGES C CXX)

set(CMAKE_C_STANDARD 23)
set(CMAKE_CXX_STANDARD 23)
set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

option(SANITIZE "Build with ASan+UBSan" OFF)
if(SANITIZE)
    set(san_flags -fsanitize=address,undefined -fno-sanitize-recover=all
                  -fno-omit-frame-pointer -g -O1)
    add_compile_options(${san_flags})
    add_link_options(${san_flags})
endif()

cmake

cmake_minimum_required(VERSION 3.28)
project(myproject LANGUAGES C CXX)

set(CMAKE_C_STANDARD 23)
set(CMAKE_CXX_STANDARD 23)
set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

option(SANITIZE "Build with ASan+UBSan" OFF)
if(SANITIZE)
    set(san_flags -fsanitize=address,undefined -fno-sanitize-recover=all
                  -fno-omit-frame-pointer -g -O1)
    add_compile_options(${san_flags})
    add_link_options(${san_flags})
endif()

Useful one-liners

实用单行命令

bash

undefined

bash

undefined

Show all optimizations enabled at -O2 (GCC)

查看-O2级别下启用的所有优化项（GCC）

gcc -Q --help=optimizers -O2 | grep enabled

Assembly output (Intel syntax)

生成汇编代码（Intel语法）

gcc -S -masm=intel -O2 foo.c -o foo.s

Preprocess and dump macros

预处理并导出宏定义

gcc -dM -E - < /dev/null

Clang optimization remarks (missed vectorization)

Clang 优化备注（未完成向量化）

clang -O2 -Rpass-missed=loop-vectorize src.c

Clang save all remarks to YAML

Clang 将所有优化备注保存为YAML

clang -O2 -fsave-optimization-record src.c

Show include search path

查看头文件搜索路径

gcc -v -E - < /dev/null 2>&1 | grep -A20 '#include <...>'

undefined

gcc -v -E - < /dev/null 2>&1 | grep -A20 '#include <...>'

undefined

Compiler-specific details

编译器专属细节

For GCC-specific flags, PGO nuances, and error patterns, see gcc.md. For Clang diagnostics, optimization remarks, macOS toolchain, and clang-tidy, see clang.md. For C++20 modules, C++23/26, and C23 features, see modern-cpp.md.

GCC专属标志、PGO细节及错误模式请参考 gcc.md。 Clang诊断信息、优化备注、macOS工具链及clang-tidy相关内容请参考 clang.md。 C++20模块、C++23/26及C23特性相关内容请参考 modern-cpp.md。