std :: basic_string :: at vs std :: basic_string ::运算符[]

std :: basic_string :: at，std :: basic_string ::运算符[]

at()和运算符[]均可用于访问字符串的元素。但是，当pos> = size时，如何处理异常条件之间存在一个区别。

• 如果pos> = size()，则std :: basic_string :: at抛出std :: out_of_range 。
• std :: bsic_string :: 运算符[]不引发异常，并产生未定义的结果。

下面是显示std :: basic_string :: at的异常处理属性的C++实现–

// C++ implementation of std::basic_string::at
#include 
#include 
  
int main()
{
    // Length = 13. Valid indices are from '0' to '12'
    std::string str = "Geeksforgeeks";
   
    // Accessing an out of bounds
    try 
    {
        // Throwing an out_of_range exception
        std::cout << str.at(13) << "\n";
    }
      
    // Error caught
    catch (std::out_of_range const& error) 
    {
        std::cout << "Exception caught" << "\n";
  
        // Printing the type of exception
        std::cout << error.what() << "\n";
    }
}

输出：

Exception caught
basic_string::at: __n (which is 13) >= this->size() (which is 13)

以下是C++实现，显示std :: basic_string ::运算符[]中没有边界检查–

// C++ implementation of std::basic_string::operator[]
#include 
#include 
  
int main()
{
    // Length = 13. Valid indices are from '0' to '12'
    std::string str = "Geeksforgeeks";
   
    // Accessing an out of bounds
    try 
    {
        //Throwing an out_of_range exception
        std::cout << str[13] << "\n";
    }
      
    // Error caught
    catch (std::out_of_range const& error) 
    {
        std::cout << "Exception caught" << "\n";
        // Printing the type of exception
        std::cout << error.what() << "\n";
    }
}

输出：

Undefined result

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