C++ Stroustrup 的 "std_lib_facilities.h"字符串结构 – 警告 : comparison of unsigned expression

Question

我正在尝试让 Stroustrup 的“std_lib_facilities.h”头文件(位于此处:http://stroustrup.com/Programming/PPP2code/std_lib_facilities.h)在 macOS Sierra、Sublime Text 3(通过构建系统)、Apple LLVM 版本 8.0.0(clang- 800.0.38)。我一直在摆弄各种设置，但无法避免两次警告，即使开头是“Hello, World!”程序正在编译运行:

std_lib_facilities.h:107:8: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
                if (i<0||size()<=i) throw Range_error(i);
                    ~^~
std_lib_facilities.h:113:8: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
                if (i<0||size()<=i) throw Range_error(i);
                    ~^~

有问题的行是以下内容的一部分:

// trivially range-checked string (no iterator checking):
struct String : std::string {
    using size_type = std::string::size_type;
//  using string::string;

    char& operator[](unsigned int i) // rather than return at(i);
    {
        if (i<0||size()<=i) throw Range_error(i);
        return std::string::operator[](i);
    }

    const char& operator[](unsigned int i) const
    {
        if (i<0||size()<=i) throw Range_error(i);
        return std::string::operator[](i);
    }
};

我的 Sublime Text C++ build设置文件是从 Can't build C++ program using Sublime Text 2 复制的在我的编译器似乎无法识别 C++11 之后，如 How do I update my compiler to use C++11 features? 中所述:

{
    "cmd": ["g++", "-Wall", "-Wextra", "-pedantic", "-std=c++11",   "${file}", "-o", "${file_path}/${file_base_name}"],
    "file_regex": "^(..[^:]*):([0-9]+):?([0-9]+)?:? (.*)$",
    "working_dir": "${file_path}",
    "selector": "source.c, source.c++",

    "variants":
    [
        {
            "name": "Run",
            "cmd": ["bash", "-c", "g++ -Wall -Wextra -pedantic -std=c++11 '${file}' -o '${file_path}/${file_base_name}' && '${file_path}/${file_base_name}'"]
        }
    ]
}

如果有人能帮助我理解为什么会出现这些警告并解决它们，我将不胜感激。

Answer 1

我会删除 i<0||部分并继续。

是的，C++之父也是人类:)