C++

參考

<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 的關係運算符
在 basic_string 物件lhs 和 rhs 之間執行適當的比較操作。

這些函式使用 basic_string::compare 進行比較，這取決於其 字元特徵 的 compare 成員。

這些運算子在標頭檔案 <string> 中過載。

引數

lhs, rhs
運算子左側和右側的引數，分別。
如果型別為charT*，則應指向一個以 null 結尾的字元序列。

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;
}

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


返回值

true如果條件成立，則為 true，並且false否則為 false。

複雜度

未指定，但通常與 lhs 和 rhs 的 長度呈線性關係。

迭代器有效性

沒有變化。

資料競爭

可以訪問兩個物件 lhs 和 rhs。

異常安全

如果型別為 char* 的引數未指向以 null 結尾的字元序列，則會導致未定義行為。
否則，如果丟擲異常，basic_string 中不會有任何更改（強保證）。
如果型別為 char* 的引數未指向以 null 結尾的字元序列，則會導致未定義行為。
對於 basic_string 物件之間的操作，永遠不會丟擲異常（無丟擲保證）。
對於其他情況，如果丟擲異常，basic_string 中不會有任何更改（強保證）。

另見

basic_string::compare
比較字串 (公共成員函式)
basic_string::find
查詢字串中第一次出現(公共成員函式)
basic_string::operator=
字串賦值 (公共成員函式)
basic_string::swap
交換字串值 (公共成員函式)