Write a function that is not defined in the STL (if it can be compiled)

Instance target: This example describes how to write a function that is not defined in the Standard Template Library STL. Here are two examples, one is to convert all data types into string to_string functions, and the other is its "inverse function" from_string function, used to convert a string to a specific type of content: in std:: The string template does not contain some functions that are more practical, because it is easy for the customer to write the code. For example, you can implement a to_string function code that converts all data types to string literals, as follows: #include &LT;IOSTREAM&GT;TEMPLATE&LT;CLASS&NBSP;T&GT;INLINE&NBSP;STD:: String to_string (Const t& value) { std::stringstream streamout; streamout< <value; return streamout.str ();} For special handling of the original data type String type Template<class t>inline std::string to_string (CONST&NBSP;STD:: String& value) { return value;} The/* function is used for all C + + data types, and for classes that support the "<<" operator, of course, it is also easy to implement functions that are opposite to the to_string function (see the following compilation results for ease)  */template<class  t>inline t from_string (Const std::string& toconvert) { std::stringstream  streamin (Toconvert);  t returnvalue=t (); streamin>>returnvalue; return  returnvalue;} The/*from_string function converts a string to a type, for example, it can convert a string to an integer but please, Mr. Schoolgirl note: From_string assumes that there is only one value in the string to be converted, any extraThe value will be ignored if I can run the program, I think I will get the result of  */int main () { int n=4; std::string str=to_string (n);   // long l=3245; str=to_string (L); n=from_string<int> ("a");  int  ntest=from_string<int> ("4354");// int ntest1=from_string<int> ("34y3");// int  ntest2=from_string<int> ("35 89");//  89 will be ignored  return 0;} --------------------Configuration: stl1 - win32 debug--------------------Compiling ... STL1. Cppc:\ accepts party \STL1. CPP (8)  : error C2079:  ' streamout '  uses undefined class  ' Basic_ Stringstream<char,struct std::char_traits<char>,class std::allocator<char> > '         c:\ accepts party \STL1. CPP (+)  : see reference to function template instantiation  ' class  std::basic_string<char,struct std::char_traits<char>,class sTd::allocator<char> > __cdecl to_string (const int &) '  being  Compiledc:\ accepts party \STL1. CPP (9)  : warning C4552:  ' << '  : operator has no effect;  expected operator with side-effect        c:\ recipient \ STL1. CPP (+)  : see reference to function template instantiation  ' class  std::basic_string<char,struct std::char_traits<char>,class std::allocator<char>  > __cdecl to_string (const int &) '  being compiledc:\ Party \stl1.cpp (10)  : error C2228: left of  '. Str '  must have class/struct/union  Type        c:\ accepts party \STL1. CPP (+)  : see reference to function template instantiation  ' class &NBSP;STD::BASIC_STRING&LT;CHAR,STRUCT&NBSP;STD:: char_traits<char>,class std::allocator<char> > __cdecl to_string (const  int &) '  being compiledc:\ accepts the party \STL1. CPP (8)  : error C2079:  ' streamout '  uses undefined class  ' Basic_ Stringstream<char,struct std::char_traits<char>,class std::allocator<char> > '         c:\ accepts party \STL1. CPP  : see reference to function template instantiation  ' class  std::basic_string<char,struct std::char_traits<char>,class std::allocator<char>  > __cdecl to_string (const long &) '  being compiledc:\ Party \stl1.cpp (9)  : warning C4552:  ' << '  : operator has no effect;  Expected operator with side-effect        c:\ recipient \ STL1. CPP ( : see&)nbsp;reference to function template instantiation  ' class std::basic_string< Char,struct std::char_traits<char>,class std::allocator<char> > __cdecl  to_string (const long &) '  being compiledc:\ receiver \STL1. CPP  : error C2228: left of  '. Str '  must have class/struct/ Union type        c:\ accepts party \STL1. CPP  : see reference to function template instantiation  ' class  std::basic_string<char,struct std::char_traits<char>,class std::allocator<char>  > __cdecl to_string (const long &) '  being compiledc:\ Party \stl1.cpp (26 )  : error C2079:  ' streamin '  uses undefined class  ' Basic_stringstream <char,struct std::char_traits<char>,class std::allocator<char>&nbsP;> '         c:\ accepts party \STL1. CPP (+)  : see reference to function template instantiation  ' int _ _cdecl from_string (Const class std::basic_string<char,struct std::char_traits<char >,class std::allocator<char> > &) '  being compiledc:\ \stl1.cpp (26)  : error C2440:  ' initializing '  : cannot convert from  ' const  class std::basic_string<char,struct std::char_traits<char>,class std::allocator< Char> > '  to  ' int '         No  User-defined-conversion operator available that can perform this conversion , or the operator cannot be called         c:\ accepts party \STL1. CPP ( : see reference to function&)nbsp;template instantiation  ' Int __cdecl from_string (const class std::basic_ string<char,struct std::char_traits<char>,class std::allocator<char> >  &) '  being compiledc:\ accepts the party \STL1. CPP  : warning C4552:  ' >> '  : operator has no effect;  expected operator with side-effect        c:\ recipient \ STL1. CPP (+)  : see reference to function template instantiation  ' int _ _cdecl from_string (Const class std::basic_string<char,struct std::char_traits<char >,class std::allocator<char> > &) '  being compilederror executing  cl.exe.stl1.exe - 6 error (s),  3 warning (s)

Write a function that is not defined in the STL (if it can be compiled)