代码来自 C++ templates 第二版:

#include <cstring>
#include <iostream>

using std::cout;
using std::endl;

// maximum of two values of any type (call-by-reference)
template <typename T>
T const &max(T const &a, T const &b)
{
    cout << "T const &max(T const &a, T const &b) called" << endl;
    return b < a ? a : b;
}

// maximum of two C-strings (call-by-value)
char const *max(char const *a, char const *b)
{
    cout << "char const *max(char const *a, char const *b) called" << endl;
    cout << a << endl;
    cout << b << endl;
    return std::strcmp(b, a) < 0 ? a : b;
}

// maximum of three values of any type (call-by-reference)
template <typename T>
T const &max(T const &a, T const &b, T const &c)
{
    return max(max(a, b), c); // error if max(a,b) uses call-by-value
}

int main()
{
    char const *s1 = "frederic";
    char const *s2 = "anica";
    char const *s3 = "lucas";
    auto m2 = ::max(s1, s2, s3); // run-time ERROR
    //!!! m2 已经是一个 dangling reference ，但是仍然得到预期结果？
    cout << m2 << endl;
}

不理解的地方在最后一行，m2 已经是一个 dangling reference ，但是为什么输出仍然得到预期结果？

编译使用的是 g++：

$ g++ --version
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
Apple clang version 12.0.0 (clang-1200.0.31.1)
Target: x86_64-apple-darwin21.1.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

编译输出：

$ g++ test2.cpp -o test2 -std=c++11    
test2.cpp:28:12: warning: returning reference to local temporary object [-Wreturn-stack-address]
    return max(max(a, b), c); // error if max(a,b) uses call-by-value
           ^~~~~~~~~~~~~~~~~
test2.cpp:36:17: note: in instantiation of function template specialization 'max<const char *>' requested here
    auto m2 = ::max(s1, s2, s3); // run-time ERROR
                ^
1 warning generated.

运行结果：

char const *max(char const *a, char const *b) called
frederic
anica

char const *max(char const *a, char const *b) called
frederic
lucas

lucas