C++字符串查找函数详解
在 C 语言和 C++ 语言中，可用于实现字符串查找功能的函数非常多。在 STL 中，字符串的查找功能可以实现多种功能，比如说：
若查找 find() 函数和其他函数没有搜索到期望的字符（或子串），则返回 npos；若搜索成功，则返回搜索到的第 1 个字符或子串的位置。其中，npos 是一个无符号整数值，初始值为 -1。当搜索失败时， npos 表示“没有找到（not found）”或“所有剩佘字符”。 值得注意的是，所有查找 find() 函数的返回值均是 size_type 类型，即无符号整数类型。该返回值用于表明字符串中元素的个数或者字符在字符串中的位置。 下面分别介绍和字符查找相关的函数。 find()函数和 rfind()find() 函数的原型主要有以下 4 种：
size_type find (value_type _Chr,size_type _Off = 0) const; find() 函数和 rfind() 函数的使用方法参见如下程序：
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string str_ch (" for");
string str (" Hi,Peter,I'm sick. Please bought some drugs for me.");
string::size_type m= str.find ('P',5);
string::size_type rm= str.rfind('P',5);
cout << "Example - find() : The position (forward) of 'P' is: " << (int) m << endl;
cout << "Example - rfind(): The position (reverse) of 'P' is: " << (int) rm << endl;
string::size_type n = str.find (" some",0);
string::size_type rn = str.rfind (" some",0);
cout << "Example - find () : The position (forward) of 'some' is: " << (int) n << endl;
cout << "Example - rfind () : The position (reverse) of 'some' is: " << (int) rn << endl;
string::size_type mo = str.find (" drugs",5);
string::size_type rmo = str.rfind (" drugs",5);
cout << "Example - find(): The position (forward) of 'drugs' is: " << (int) mo << endl;
cout << "Example - rfind(): The position (reverse) of 'drugs' is: " << (int) rmo << endl;
string::size_type no = str.find (str_ch,0);
string::size_type rno = str.rfind(str_ch,0);
cout << "Example - find (): The position of 'for' is: " << (int) no << endl;
cout << "Example - rfind(): The position of 'for' is: " << (int) rno << endl;
cin.get ();
}
程序的运行结果为：
Example - find() : The position (forward) of 'P' is: 5 find_first_of()函数和 find_last_of()函数find_first_of() 函数可实现在源串中搜索某字符串的功能，该函数的返回值是被搜索字符串的第 1 个字符第 1 次出现的下标（位置）。若查找失败，则返回 npos。find_last_of() 函数同样可实现在源串中搜索某字符串的功能。与 find_first_of() 函数所不同的是，该函数的返回值是被搜索字符串的最后 1 个字符的下标（位置）。若查找失败，则返回 npos。 上述两个函数的原型分别为：
size_type find_first_not_of (value_type_Ch,size_type_Off = 0) const; size_type find_first_of (const value_type* _Ptr,size_type _Off = 0) const;
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string str_ch ("for");
string str("Hi,I'm sick. Please bought some drugs for me. ");
int length = str.length();
string::size_type m = str.find_first_of ('P',0);
string::size_type rm = str.find_last_of ('P',(length - 1));
cout << "Example - find_first_of (): The position (forward) of 'P' is: " << (int) m << endl;
cout << "Example - find_last_of (): The position (reverse) of 'P' is： " << (int) rm << endl;
string:: size_type n = str.find_first_of ("some",0);
string:: size_type rn = str.find_last_of ("some",(length -1));
cout << "Example - find_first_of(): The position (forward) of 'some' is: " << (int) n << endl;
cout << "Example - find_last_of(): The position (reverse) of 'some' is: " << (int) rn << endl;
string:: size_type mo = str.find_first_of ("drugs",5);
string:: size_type rmo = str.find_last_of ("drugs",(length-1),5);
cout << "Example - find_first_of () : The position (forward) of 'drugs' is: " << (int) mo << endl;
cout << "Example - find_last_of () : The position (reverse) of 'drugs' is: " << (int) rmo << endl;
string::size_type no = str.find_first_of (str_ch,0);
string::size_type rno = str.find_last_of (str_ch,(length -1));
cout << "Example - find_first_of() : The position of 'for' is: " << (int) no << endl;
cout << "Example - find_last_of () : The position of 'for' is: " << (int) rno << endl;
cin.get();
return 0;
}
程序执行结果：
Example - find_first_of (): The position (forward) of 'P' is: 4 find_first_not_of()函数和 find_last_not_of()函数find_first_not_of() 函数的函数原型为：
size_type find_first_not_of (value_type _Ch,size_type_Off = 0) const;
#include < iostream >
#include <string>
using namespace std;
int main ()
{
string str_ch (" for");
string str ("Hi,I'm sick. Please bought some drugs for me.");
int length = str.length ();
string::size_type m= str.find_first_not_of ('P',0);
string::size_type rm= str.find_last_not_of ('P',(length -1);
cout << "Example - find_first_of (): The position (forward) of 'P' is: " << (int) m << endl;
cout << "Example - find_last_of (): The position (reverse) of 'P' is: " << (int) rm << endl;
string:: size_type n = str.find_first_not_of ("some",0);
string:: size_type rn = str.find_last_not_of ("some",(length -1));
cout << "Example - find_first_of (): The position (forward) of 'some' is: " << (int) n << endl;
cout << "Example - find_last_of (): The position (reverse) of 'some' is: " << (int) rn << endl;
string:: size_type mo = str.find_first_not_of ("drugs",5);
string:: size_type rmo = str.find_last_not_of ("drugs",5);
cout << "Example - find_first_of (): The position (forward) of 'drugs' is: " << (int) mo << endl;
cout << "Example - find_last_of (): The position (reverse) of 'drugs' is: " << (int) rno << endl;
string::size_type no = str.find_first_not_of (str_ch,0);
string::size_type rno = str.find_last_not_of (str_ch,(length-1));
cout << "Example - find_first_of (): The position of 'for' is: " << (int) no << endl;
cout << "Example - find_last_of () : The position of 'for' is: " << (int) rno << endl;
cin.get ();
return 0;
}
程序运行结果为：
Example - find_first_of (): The position (forward) of 'P' is: 0 （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |