C语言-Werror=sign-compare编译错误解决方案

Posted 2022-01-17 coffee tea or me

在做C语言的一个小测试时，写了下面的一段代码，涉及到有符号数和无符号数的大小比较。

// automatic type conversion
if (-1L < 1U)

        printf("sizeof(unsigned int)=%lu\\nsizeof(signed long int)=%lu\\n",
               sizeof(unsigned int), sizeof(signed long int));
        printf("\\\'-1L<1U\\\' since unsigned int is promoted to signed long type!\\n");

if (-1L > 1UL)

        printf("sizeof(signed long int)=%lu\\nsizeof(unsigned long int)=%lu\\n",
               sizeof(signed long int), sizeof(unsigned long int));
        printf("\\\'-1L>1UL\\\' since signed long int is promoted to unsigned type!\\n");

然后使用CMake编译时显示错误

/home/cv/playground_test/src/playground.cc:185:10: In function‘int main(int, const char**)’:
error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
  if (-1L > 1UL)
      ~~~~^~~~~
cc1plus: all warnings being treated as errors
CMakeFiles/playground.dir/build.make:62: recipe for target \'CMakeFile
s/playground.dir/src/playground.c.o\' failed

有符号数与无符号数的比较，虽然有时确实需要特别注意，但也不至于上来就Fatal Error，尤其当我们明确需要这样操作时。

-Werror是gcc/g++的配置参数，执行严格的错误检查，这里显然是把一般的警告也作为错误对待了，在CMakeLists中将其去掉即可。

选项	说明
-Wall	打开一些必要的警告选项，建议编译时加此选项。
-Werror	视警告为错误，出现任何警告即放弃编译。
-Wextra	打印一些额外的警告信息。
-w	禁止显示所有警告信息。

把如下展示的第11行

set(CMAKE_CXX_FLAGS "$CMAKE_CXX_FLAGS -Wall -Werror")

替换成

set(CMAKE_CXX_FLAGS "$CMAKE_CXX_FLAGS -Wall")

然后重新编译就不会报错了。

修改后的CMakeLists.txt文件内容如下

01 cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
02 project(playground)
03
04 #====================================================
05 ## C++ compiler options
06 #====================================================
07 set(CMAKE_CXX_STANDARD 11)
08 set(CMAKE_CXX_EXTENSIONS OFF)
09 set(CMAKE_CXX_STANDARD_REQUIRED ON)
10 set(CMAKE_C_FLAGS "$CMAKE_C_FLAGS -std=c99 -Wall")
11 #set(CMAKE_CXX_FLAGS "$CMAKE_CXX_FLAGS -Wall -Werror")
12 set(CMAKE_CXX_FLAGS "$CMAKE_CXX_FLAGS -Wall")
13
14 set(CMAKE_BUILD_TYPE RELEASE)
15 # Set output directory to store executables, create if not exist
16 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY $CMAKE_CURRENT_SOURCE_DIR/bin)
17
18 ## Search for source files
19 set(SRC_DIR $CMAKE_CURRENT_SOURCE_DIR/src)
20 file(GLOB_RECURSE SRC_LIST "$SRC_DIR/[^.]*.c*")
21
22 #====================================================
23 ## Compile target executables
24 #====================================================
25 foreach(src $SRC_LIST)
26         string(REGEX REPLACE ".+/(.+)\\\\..*" "\\\\1" SRC_FILE_NAME $src)
27         add_executable($SRC_FILE_NAME $src)
28         set_target_properties($SRC_FILE_NAME PROPERTIES LINKER_LANGUAGE CXX)
29         target_link_libraries($SRC_FILE_NAME pthread)
30 endforeach(src $SRC_LIST)

工程目录结构和运行主机配置如下。

# Project tree structure
.
├── CMakeLists.txt
├── bin
│   └── playground
├── build
└── src
    └── playground.c

# Linux Ubuntu system information
cv@cv:~$ uname -a
Linux cv 4.18.0-25-generic #26~18.04.1-Ubuntu SMP Thu Jun 27 07:28:31 UTC 2019
x86_64 x86_64 x86_64 GNU/Linux

cv@cv:~$ g++ --version
g++ (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

cv@cv:~$ cmake --version
cmake version 3.10.2
CMake suite maintained and supported by Kitware (kitware.com/cmake)

cv@cv:~$ make --version
GNU Make 4.1
Built for x86_64-pc-linux-gnu
Copyright (C) 1988-2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

这里只是摘出相关的部分进行记录和说明，完整测试代码及环境要求详见 https://github.com/philleer/leetcode_test/tree/dev 。

（全文完）

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本文作者 ：phillee
发表日期 ：2022年01月16日
本文链接 ：https://www.cnblogs.com/phillee/p/15810793.html
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限于本人水平，如果文章和代码有表述不当之处，还请不吝赐教。