c++ - template specialization call by reference -

to understand more c++ templates, reading book (c++ templates : complate guide) , can't understand explanation.

// basics/max3a.cpp #include <iostream> #include <cstring> #include <string>  // maximum of 2 values of type (call-by-reference) template <typename t> inline t const& max (t const& a, t const& b) {     return < b ? b : a; }  // maximum of 2 c-strings (call-by-value) inline char const* max (char const* a, char const* b) {     return std::strcmp(a,b) < 0 ? b : a; }  // maximum of 3 values of 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 } 

the book says,

" problem if call max() 3 c-strings, statement

return max (max(a,b), c); 

becomes error. because c-strings, max(a,b) creates new, temporary local value may returned function reference.
"

i understand max(s1, s2, s3) called reference arguments, inside max-of-three function, max(a,b) using call-by-value function(because it's more speicialized). , temporary return value max(a,b) value(in stack) , there no max(value, reference) function. isn't problem? can't understand book's text saying ... becomes error. because c-strings, max(a,b) creates new, temporary local value may returned function reference.

and temporary return value max(a,b) value(in stack)

no, return value not "in stack". it's value, period. full stop:

inline char const* max (char const* a, char const* b) 

this returns value. in caller's context, it's temporary value. now, let's proceed next step:

return max (max(a,b), c); // 

in template, return returns reference. refence value returned call max(), which, in context, temporary value.

this temporary value goes out of scope , gets destroyed when function call returns. does, , returns reference destroyed value. de-referencing reference becomes undefined behavior.

this has nothing templates, , specialization. true equivalent, non-template code.