C++

参考

<string>

basic_string

function template
<string>

std::relational operators (basic_string)

(1)
template <class charT, class traits, class Alloc>  bool operator== (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator== (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator== (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(2)
template <class charT, class traits, class Alloc>  bool operator!= (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator!= (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator!= (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(3)
template <class charT, class traits, class Alloc>  bool operator<  (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator<  (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator<  (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(4)
template <class charT, class traits, class Alloc>  bool operator<= (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator<= (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator<= (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(5)
template <class charT, class traits, class Alloc>  bool operator>  (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator>  (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator>  (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(6)
template <class charT, class traits, class Alloc>  bool operator>= (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator>= (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator>= (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(1)
template <class charT, class traits, class Alloc>  bool operator== (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs) noexcept;template <class charT, class traits, class Alloc>  bool operator== (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator== (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(2)
template <class charT, class traits, class Alloc>  bool operator!= (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs) noexcept;template <class charT, class traits, class Alloc>  bool operator!= (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator!= (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(3)
template <class charT, class traits, class Alloc>  bool operator<  (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs) noexcept;template <class charT, class traits, class Alloc>  bool operator<  (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator<  (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(4)
template <class charT, class traits, class Alloc>  bool operator<= (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs) noexcept;template <class charT, class traits, class Alloc>  bool operator<= (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator<= (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(5)
template <class charT, class traits, class Alloc>  bool operator>  (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs) noexcept;template <class charT, class traits, class Alloc>  bool operator>  (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator>  (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
(6)
template <class charT, class traits, class Alloc>  bool operator>= (const basic_string<charT,traits,Alloc>& lhs,                   const basic_string<charT,traits,Alloc>& rhs) noexcept;template <class charT, class traits, class Alloc>  bool operator>= (const charT* lhs, const basic_string<charT,traits,Alloc>& rhs);template <class charT, class traits, class Alloc>  bool operator>= (const basic_string<charT,traits,Alloc>& lhs, const charT* rhs);
basic_string 的关系运算符
在 basic_string 对象lhs 和 rhs 之间执行适当的比较操作。

这些函数使用 basic_string::compare 进行比较，这取决于其 字符特征 的 compare 成员。

这些运算符在头文件 <string> 中重载。

参数

lhs, rhs
运算符左侧和右侧的参数，分别。
如果类型为charT*，则应指向一个以 null 结尾的字符序列。

示例

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// string comparisons
#include <iostream>
#include <vector>

int main ()
{
  std::string foo = "alpha";
  std::string bar = "beta";

  if (foo==bar) std::cout << "foo and bar are equal\n";
  if (foo!=bar) std::cout << "foo and bar are not equal\n";
  if (foo< bar) std::cout << "foo is less than bar\n";
  if (foo> bar) std::cout << "foo is greater than bar\n";
  if (foo<=bar) std::cout << "foo is less than or equal to bar\n";
  if (foo>=bar) std::cout << "foo is greater than or equal to bar\n";

  return 0;
}

输出
foo and bar are not equal
foo is less than bar
foo is less than or equal to bar


返回值

true如果条件成立，则为 true，并且false否则为 false。

复杂度

未指定，但通常与 lhs 和 rhs 的 长度呈线性关系。

迭代器有效性

没有变化。

数据竞争

可以访问两个对象 lhs 和 rhs。

异常安全

如果类型为 char* 的参数未指向以 null 结尾的字符序列，则会导致未定义行为。
否则，如果抛出异常，basic_string 中不会有任何更改（强保证）。
如果类型为 char* 的参数未指向以 null 结尾的字符序列，则会导致未定义行为。
对于 basic_string 对象之间的操作，永远不会抛出异常（无抛出保证）。
对于其他情况，如果抛出异常，basic_string 中不会有任何更改（强保证）。

另见

basic_string::compare
比较字符串 (公共成员函数)
basic_string::find
查找字符串中第一次出现(公共成员函数)
basic_string::operator=
字符串赋值 (公共成员函数)
basic_string::swap
交换字符串值 (公共成员函数)