使用gettext实现C++国际化：如何让字符串在定义阶段完成翻译？

问题背景 #

使用gettext进行C++国际化开发时，定义的静态字符串A::BASE_PCB和非静态字符串BASE_PCB_2，在定义阶段用__()包裹后并未完成翻译，只有在运行时再次用__()包裹才能得到正确结果。需要实现字符串在定义阶段就完成翻译。

代码与配置示例 #

main.cpp #

#include <iostream>
#include <string>
#include <libintl.h>

#define __(String) gettext(String)

class A {
public:
    static const std::string BASE_PCB;
};

const std::string A::BASE_PCB = __("BasePCB");

int main() {
    std::string BASE_PCB_2 = __("BasePCB2");

    const std::string path = "/usr/local/share/locale";
    std::cout << "Locale path: " << path << std::endl;

    setlocale(LC_ALL, "fr_CH.utf8");
    bindtextdomain("example", path.c_str());
    textdomain("example");

    std::cout << "Locale: " << setlocale(LC_ALL, nullptr) << std::endl;

    std::cout << "1. Translation: " << A::BASE_PCB.c_str() << std::endl;
    std::cout << "2. Translation with __: " << __(A::BASE_PCB.c_str()) << std::endl;
    std::cout << "3. Translation: " << BASE_PCB_2 << std::endl;
    std::cout << "4. Translation with __: " << __(BASE_PCB_2.c_str()) << std::endl;
    return 0;
}

fr.po #

#: main.cpp:12
msgid "BasePCB"
msgstr "Base PCB"

#: main.cpp:15
msgid "BasePCB2"
msgstr "Base PCB 2"

.mo文件生成与部署命令 #

msgfmt fr.po -o example.mo
cp example.mo /usr/local/share/locale/fr/LC_MESSAGES/example.mo

CMakeLists.txt #

cmake_minimum_required(VERSION 3.8)

project (
 "CppInternationalization"
 VERSION 1.0.0
 LANGUAGES CXX
)

# 使用C++20
set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

add_executable(${PROJECT_NAME} "main.cpp")

# 添加libintl
find_package(Intl REQUIRED)
target_link_libraries(${PROJECT_NAME} PUBLIC ${Intl_LIBRARY})
target_include_directories(${PROJECT_NAME} PUBLIC ${Intl_INCLUDE_DIRS})

执行命令 #

mkdir build
cmake .. && cmake --build . && ./CppInternationalization

当前输出结果 #

Locale path: /usr/local/share/locale
Locale: fr_CH.utf8
1. Translation: BasePCB  # <- 预期结果为'Base PCB'
2. Translation with __: Base PCB
3. Translation: BasePCB2  # <- 预期结果为'Base PCB 2'
4. Translation with __: Base PCB 2

问题原因 #

C++中，静态成员变量A::BASE_PCB的初始化发生在main()函数执行之前，而setlocale、bindtextdomain、textdomain这些gettext核心配置函数都在main()内调用。此时gettext未完成本地化环境初始化，无法加载翻译文件，定义阶段调用__()只能得到原字符串。

非静态的BASE_PCB_2虽然在main()内定义，但初始化时机早于gettext配置函数执行，同样无法完成翻译。

解决方案 #

要让字符串在定义/初始化阶段完成翻译，必须确保gettext的初始化逻辑在字符串初始化之前执行，以下两种方法可实现：

方法1：全局静态初始化类（推荐） #

将gettext初始化逻辑封装到全局静态类中，利用C++静态对象初始化顺序，让配置逻辑先于目标字符串执行：

修改后的main.cpp：

#include <iostream>
#include <string>
#include <libintl.h>

#define __(String) gettext(String)

// 全局初始化类，确保gettext配置先执行
class GettextInitializer {
public:
    GettextInitializer() {
        const std::string path = "/usr/local/share/locale";
        setlocale(LC_ALL, "fr_CH.utf8");
        bindtextdomain("example", path.c_str());
        textdomain("example");
    }
};

// 全局静态对象，在main之前初始化
static GettextInitializer gettext_init;

class A {
public:
    static const std::string BASE_PCB;
};

const std::string A::BASE_PCB = __("BasePCB");

int main() {
    // 此时gettext已初始化完成
    std::string BASE_PCB_2 = __("BasePCB2");

    const std::string path = "/usr/local/share/locale";
    std::cout << "Locale path: " << path << std::endl;

    std::cout << "Locale: " << setlocale(LC_ALL, nullptr) << std::endl;

    std::cout << "1. Translation: " << A::BASE_PCB.c_str() << std::endl;
    std::cout << "2. Translation with __: " << __(A::BASE_PCB.c_str()) << std::endl;
    std::cout << "3. Translation: " << BASE_PCB_2 << std::endl;
    std::cout << "4. Translation with __: " << __(BASE_PCB_2.c_str()) << std::endl;
    return 0;
}

方法2：延迟字符串初始化 #

将静态成员变量改为函数内的静态变量，或在gettext初始化完成后再初始化字符串：

修改后的main.cpp示例：

#include <iostream>
#include <string>
#include <libintl.h>

#define __(String) gettext(String)

class A {
public:
    // 改为静态函数，第一次调用时初始化
    static const std::string& BASE_PCB() {
        static const std::string val = __("BasePCB");
        return val;
    }
};

int main() {
    const std::string path = "/usr/local/share/locale";
    std::cout << "Locale path: " << path << std::endl;

    setlocale(LC_ALL, "fr_CH.utf8");
    bindtextdomain("example", path.c_str());
    textdomain("example");

    // 在gettext初始化后再初始化字符串
    std::string BASE_PCB_2 = __("BasePCB2");

    std::cout << "Locale: " << setlocale(LC_ALL, nullptr) << std::endl;

    std::cout << "1. Translation: " << A::BASE_PCB().c_str() << std::endl;
    std::cout << "2. Translation with __: " << __(A::BASE_PCB().c_str()) << std::endl;
    std::cout << "3. Translation: " << BASE_PCB_2 << std::endl;
    std::cout << "4. Translation with __: " << __(BASE_PCB_2.c_str()) << std::endl;
    return 0;
}

验证结果 #

修改后执行程序，输出会变为：

Locale path: /usr/local/share/locale
Locale: fr_CH.utf8
1. Translation: Base PCB
2. Translation with __: Base PCB
3. Translation: Base PCB 2
4. Translation with __: Base PCB 2

内容的提问来源于stack exchange，提问作者Molitoris