C++ Tutorial/template/template pointer parameter — различия между версиями
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Версия 14:21, 25 мая 2010
template function for reference parameters
/* The following code example is taken from the book
* "C++ Templates - The Complete Guide"
* by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
*
* (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <string>
// note: reference parameters
template <typename T>
inline T const& max (T const& a, T const& b)
{
return a < b ? b : a;
}
int main()
{
std::string s;
::max("apple","peach"); // OK: same type
//::max("apple","tomato"); // ERROR: different types
//::max("apple",s); // ERROR: different types
}template function to get maximum of two pointers
/* The following code example is taken from the book
* "C++ Templates - The Complete Guide"
* by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
*
* (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <cstring>
#include <string>
// maximum of two values of any type
template <typename T>
inline T const& max (T const& a, T const& b)
{
return a < b ? b : a;
}
// maximum of two pointers
template <typename T>
inline T* const& max (T* const& a, T* const& b)
{
return *a < *b ? b : a;
}
// maximum of two C-strings
inline char const* const& max (char const* const& a,
char const* const& b)
{
return std::strcmp(a,b) < 0 ? b : a;
}
int main ()
{
int a=7;
int b=42;
std::cout<<"\n\n" << ::max(a,b); // max() for two values of type int
std::string s="hey";
std::string t="you";
std::cout<<"\n\n" << ::max(s,t); // max() for two values of type std::string
int* p1 = &b;
int* p2 = &a;
std::cout<<"\n\n" << ::max(p1,p2); // max() for two pointers
char const* s1 = "David";
char const* s2 = "Nico";
std::cout<<"\n\n" << ::max(s1,s2); // max() for two C-strings
}42 you 0x22ff58 Nico"
template function with pointer parameter
/* The following code example is taken from the book
* "C++ Templates - The Complete Guide"
* by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
*
* (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
template <typename T>
inline
T accum (T const* beg, T const* end)
{
T total = T(); // assume T() actually creates a zero value
while (beg != end) {
total += *beg;
++beg;
}
return total;
}
int main()
{
// create array of 5 integer values
int num[] = { 1, 2, 3, 4, 5 };
// print average value
std::cout << "the average value of the integer values is "
<< accum(&num[0], &num[5]) / 5
<< "\n";
// create array of character values
char name[] = "templates";
int length = sizeof(name)-1;
// (try to) print average character value
std::cout << "the average value of the characters in \""
<< name << "\" is "
<< accum(&name[0], &name[length]) / length
<< "\n";
}the average value of the integer values is 3 the average value of the characters in "templates" is -5
