In Chapter 2 Function Template of the book C++ templates, 1st Edition, there is a code example which the book say it has problem:

#include <iostream>
#include <cstring>
#include <string>

// maximum of two values of any type (call-by-reference)
template <typename T>
inline T const& max (T const& a, T const& b)
{
    printf("call 1 n");
    return  a < b  ?  b : a;
}

// maximum of two C-strings (call-by-value)
inline char const* max (char const* a, char const* b)
{ 
    printf("call 2 %s %sn", a, b);
    return  std::strcmp(a,b) < 0  ?  b : a;
}

// maximum of three values of any type (call-by-reference)
template <typename T>
inline 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 ()
{
    //::max(7, 42, 68);     // OK

    const char* s1 = "frederic";
    const char* s2 = "anica";
    const char* s3 = "lucas";
    ::max(s1, s2, s3);    // ERROR
    printf("finish");

}

I try it on compiler explorer, it can work, although there is compiler warning:

<source>:24:16: warning: returning reference to temporary [-Wreturn-local-addr]
   24 |     return max (max(a,b), c);  // error, if max(a,b) uses call-by-value
      |            ~~~~^~~~~~~~~~~~~

I can’t understand what it means for “returning reference to temporary”. Does it mean max(a,b) return reference to temporary? For this example, as the passed char* pointer is always valid, any potential problem here?

Thanks