C++字符串查找函数详解
- 搜索单个字符、搜索子串;
- 实现前向搜索、后向搜索;
- 分别实现搜索第一个和最后一个满足条件的字符(或子串);
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()函数的第1个参数是被搜索的字符、第2个参数是在源串中开始搜索的下标位置
size_type find (const value_type* _Ptr , size_type _Off = 0) const;
//find()函数的第1个参数是被搜索的字符串,第2个参数是在源串中开始搜索的下标位置
size_type find (const value_type* _Ptr, size_type _Off = 0, size_type _Count) const;
//第1个参数是被搜索的字符串,第2个参数是源串中开始搜索的下标,第3个参数是关于第1个参数的字符个数,可能是 _Ptr 的所有字符数,也可能是 _Ptr 的子串宇符个数
size_type find (const basic_string& _Str, size_type _Off = 0) const;
//第1个参数是被搜索的字符串,第2参数是在源串中开始搜索的下标位置
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", 0, 5); string::size_type rmo = str.rfind (" drugs", 0, 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
Example - rfind(): The position (reverse) of 'P' is: 5
Example - find () : The position (forward) of 'some' is: 35
Example - rfind () : The position (reverse) of 'some' is: -1
Example - find(): The position (forward) of 'drugs' is: 40
Example - rfind(): The position (reverse) of 'drugs' is: -1
Example - find (): The position of 'for' is: 46
Example - rfind(): The position of 'for' is: -1
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;
size_type find_first_of (const value_type* _Ptr, size_type_Off, size_type_Count) const;
size_type find_first_of (const basic_string & _Str, size_type_Off = 0) const;
size_type find_last_of (value_type _Ch, size_type_Off = npos) const;
size_type find_last_of (const value_type* _Ptr, size_type_Off = npos) const;
size_type find_last_of (const value_type* _Ptr, size_type _Off, size_type _Count) const;
size_type find_last_of (const basic_string& _Str, size_type_Off = npos) const;
#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. "); 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", 0, 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
Example - find_last_of (): The position (reverse) of 'P' is: 21
Example - find_first_of(): The position (forward) of 'some' is: 5
Example - find_last_of(): The position (reverse) of 'some' is: 51
Example - find_first_of () : The position (forward) of 'drugs' is: 8
Example - find_last_of () : The position (reverse) of 'drugs' is: 48
Example - find_first_of() : The position of 'for' is: 8
Example - find_last_of () : The position of 'for' is: 48
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;
size_type find_first_not_of (const value_type * _Ptr, size_type_Off = 0) const;
size_type find_first_not_of (const value_type* _Ptr, size_type_Off, size_type_Count) const;
size_type find_first_not_of (const basic_string & _Str, size_type_Off = 0) const;
#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."); 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", 0, 5); string:: size_type rmo = str.find_last_not_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) 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
Example - find_last_of (): The position (reverse) of 'P' is: 52
Example - find_first_of (): The position (forward) of 'some' is: 0
Example - find_last_of (): The position (reverse) of 'some' is: 52
Example - find_first_of (): The position (forward) of 'drugs' is: 0
Example - find_last_of (): The position (reverse) of 'drugs' is: 52
Example - find_first_of (): The position of 'for' is: 0
Example - find_last_of () : The position of 'for' is: 52
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