C++ std::string::substr()函数（生成子串）

Posted 2022-05-17 Dontla

文章目录

• • cppman -f std::string::substr
  • 上面文档中的代码示例

cppman -f std::string::substr

std::string::substr(3)                                                C++ Programmer's Manual                                                std::string::substr(3)



NAME
       std::string::substr - Generate substring	//生成子串

TYPE
       public member function

SYNOPSIS
       #include <string>

       string substr (size_t pos = 0, size_t len = npos) const;

DESCRIPTION
       Returns a newly constructed string object with its value initialized to a copy of a substring of this object.
       The  substring  is the portion of the object that starts at character position pos and spans len characters (or until the end of the string, whichever comes
       first).
       //返回一个新构造的字符串对象，其值初始化为此对象的子字符串的副本。
        //子字符串是从字符位置 pos 开始并跨越 len 个字符（或直到字符串末尾，以先到者为准）的对象部分。

PARAMETERS
       pos    Position of the first character to be copied as a substring.
              If this is equal to the string length, the function returns an empty string.
              If this is greater than the string length, it throws out_of_range.
              Note: The first character is denoted by a value of 0 (not 1).
              //要作为子字符串复制的第一个字符的位置。
               //如果这等于字符串长度，则该函数返回一个空字符串。
               //如果这大于字符串长度，则抛出 out_of_range。
               //注意：第一个字符由值 0（不是 1）表示。

       len    Number of characters to include in the substring (if the string is shorter, as many characters as possible are used).
              A value of string::npos indicates all characters until the end of the string.
              size_t is an unsigned integral type (the same as member type string::size_type).
              //要包含在子字符串中的字符数（如果字符串较短，则使用尽可能多的字符）。
               //string::npos 的值表示直到字符串结尾的所有字符。
               //size_t 是无符号整数类型（与成员类型 string::size_type 相同）。

RETURN VALUE
       A string object with a substring of this object.
       //带有此对象的子字符串的字符串对象。

EXAMPLE
         // string::substr
         #include <iostream>
         #include <string>
         int main ()
         
           std::string str="We think in generalities, but we live in details.";
                                                    // (quoting Alfred N. Whitehead)
           std::string str2 = str.substr (3,5);     // "think"
           std::size_t pos = str.find("live");      // position of "live" in str
           std::string str3 = str.substr (pos);     // get from "live" to the end
           std::cout << str2 << ' ' << str3 << '\\n';
           return 0;
         

       Output:
         think live in details.


COMPLEXITY
       Unspecified, but generally linear in the length of the returned object.

ITERATOR VALIDITY
       No changes.

DATA RACES
       The object is accessed.

EXCEPTION SAFETY
       Strong guarantee: if an exception is thrown, there are no changes in the string.
       If pos is greater than the string length, an out_of_range exception is thrown.
       A bad_alloc exception is thrown if the function needs to allocate storage and fails.

SEE ALSO
       string::replace(3)
              Replace portion of string  (public member function)

       string::data(3)
              Get string data  (public member function)

       string::find(3)
              Find content in string  (public member function)

       string::assign(3)
              Assign content to string  (public member function)

       string::string(3)
              Construct string object  (public member function)

REFERENCE
       cplusplus.com, 2000-2015 - All rights reserved.



cplusplus.com                                                                2022-05-13                                                      std::string::substr(3)
(END)

上面文档中的代码示例

（VS中运行）

#pragma warning(disable : 4996)
// string::substr
#include <iostream>
#include <string>
int main()

    std::string str = "We think in generalities, but we live in details.";  //“我们思考一般性，但我们生活在细节中。”
    // (quoting Alfred N. Whitehead)
    std::string str2 = str.substr(3, 5);     // "think"
    std::size_t pos = str.find("live");      // position of "live" in str
    std::string str3 = str.substr(pos);     // get from "live" to the end
    std::cout << str2 << ' ' << str3 << '\\n';
    return 0;

运行结果：

think live in details.