STL的algorithm庫確實給我們提供了這樣的便利，使用模板函式transform可以輕鬆解決這個問題，開發人員只需要提供一個函式物件，例如將char轉成大寫的toupper函式或者小寫的函式tolower函式。

transform原型：

1. template < class InputIterator, class OutputIterator, class UnaryOperator >  
2.   OutputIterator transform ( InputIterator first1, InputIterator last1,  
3.                              OutputIterator result, UnaryOperator op );  
4. template < class InputIterator1, 
   class InputIterator2,  
5.            class OutputIterator, class BinaryOperator >  
6.   OutputIterator transform ( InputIterator1 first1, InputIterator1 last1,  
7.                              InputIterator2 first2, OutputIterator result,  
8.                              BinaryOperator binary_op );  

template < class InputIterator, class OutputIterator, class UnaryOperator >
  OutputIterator transform ( InputIterator first1, InputIterator last1,
                             OutputIterator result, UnaryOperator op );

template < class InputIterator1, class InputIterator2,
           class OutputIterator, class BinaryOperator >
  OutputIterator transform ( InputIterator1 first1, InputIterator1 last1,
                             InputIterator2 first2, OutputIterator result,
                             BinaryOperator binary_op );
 

1. #include <string>
2. #include <algorithm>
3. usingnamespace std;  
4. int main()  
5. {  
6.     string strA = "[email protected]";  
7.     string strB = "[email protected]";  
8.     printf("Before transform:\n");  
9.     printf("strA:%s \n", strA.c_str());  
10.     printf("strB:%s \n\n", strB.c_str());  
11.     transform(strA.begin(), strA.end(), strA.begin(), ::toupper);  
12.     transform(strB.begin(), strB.end(), strB.begin(), ::toupper);  
13.     printf("After transform to toupper:\n");  
14.     printf("strA:%s \n", strA.c_str());  
15.     printf("strB:%s \n\n", strB.c_str());  
16.     transform(strA.begin(), strA.end(), strA.begin(), ::tolower);  
17.     transform(strB.begin(), strB.end(), strB.begin(), ::tolower);  
18.     printf("After transform to lower:\n");  
19.     printf("strA:%s \n", strA.c_str());  
20.     printf("strB:%s \n\n", strB.c_str());  
21.     return 0;  
22. }  

#include <string>
#include <algorithm>
using namespace std;

int main()
{
    string strA = "[email protected]";
    string strB = "[email protected]";
    printf("Before transform:\n");
    printf("strA:%s \n", strA.c_str());
    printf("strB:%s \n\n", strB.c_str());

    transform(strA.begin(), strA.end(), strA.begin(), ::toupper);
    transform(strB.begin(), strB.end(), strB.begin(), ::toupper);
    printf("After transform to toupper:\n");
    printf("strA:%s \n", strA.c_str());
    printf("strB:%s \n\n", strB.c_str());

    transform(strA.begin(), strA.end(), strA.begin(), ::tolower);
    transform(strB.begin(), strB.end(), strB.begin(), ::tolower);
    printf("After transform to lower:\n");
    printf("strA:%s \n", strA.c_str());
    printf("strB:%s \n\n", strB.c_str());
    return 0;
}

執行結果：

1. strA:[email protected]   
2. strB:[email protected]   
3. After transform to toupper:  
4. strA:[email protected]   
5. strB:[email protected]   
6. After transform to lower:  
7. strA:[email protected]   
8. strB:[email protected]   

strA:[email protected] 
strB:[email protected] 

After transform to toupper:
strA:[email protected] 
strB:[email protected] 

After transform to lower:
strA:[email protected] 
strB:[email protected]