c++ string 全部转化为大写/小写的函数

将一个string转换成大写或者小写，是项目中经常需要做的事情，但string类里并 没有提供这个方法。自己写个函数来实现。STL的algorithm库给我们提供了这样的便利，使用模板函数transform可以解决这个问题

transform函数原型

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 );

实例

#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;  
}

运行结果

strA:yasaken@126.com   
strB:LURY@LENOVO.com   
  
After transform to toupper:  
strA:YASAKEN@126.COM   
strB:LURY@LENOVO.COM   
  
After transform to lower:  
strA:yasaken@126.com   
strB:lury@lenovo.com