C++ 中用于实现字符串查找功能的函数

在 STL 中，字符串的查找功能可以实现多种功能，比如说： 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。

//find()函数和 rfind()： //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 //rfind() 函数的原型和find()函数的原型类似，参数情况也类似。只不过 rfind() 函数适用于实现逆向查找。 #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 << "find() : The position (forward) of 'P' is: " << (int) m << endl; cout << "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 << "find () : The position (forward) of 'some' is: " << (int) n << endl; cout << "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 << "find(): The position (forward) of 'drugs' is: " << (int) mo << endl; cout << "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 << "find (): The position of 'for' is: " << (int) no << endl; cout << "rfind(): The position of 'for' is: " << (int) rno << endl; cin.get (); } //程序的运行结果为： //find() : The position (forward) of 'P' is: 5 //rfind(): The position (reverse) of 'P' is: 5 //find () : The position (forward) of 'some' is: 35 //rfind () : The position (reverse) of 'some' is: -1 //find(): The position (forward) of 'drugs' is: 40 //rfind(): The position (reverse) of 'drugs' is: -1 //find (): The position of 'for' is: 46 //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。

find_first_of 函数最容易出错的地方是和find函数搞混。它最大的区别就是如果在一个字符串str1中查找另一个字符串str2，如果str1中含有str2中的任何字符，则就会查找成功，而find则不同

//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 << "find_first_of (): The position (forward) of 'P' is: " << (int) m << endl; cout << "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 << "find_first_of(): The position (forward) of 'some' is: " << (int) n << endl; cout << "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 << "find_first_of () : The position (forward) of 'drugs' is: " << (int) mo << endl; cout << "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 << "find_first_of() : The position of 'for' is: " << (int) no << endl; cout << "find_last_of () : The position of 'for' is: " << (int) rno << endl; cin.get(); return 0; } //程序执行结果： //find_first_of (): The position (forward) of 'P' is: 4 //find_last_of (): The position (reverse) of 'P' is： 21 //find_first_of(): The position (forward) of 'some' is: 5 //find_last_of(): The position (reverse) of 'some' is: 51 //find_first_of () : The position (forward) of 'drugs' is: 8 //find_last_of () : The position (reverse) of 'drugs' is: 48 //find_first_of() : The position of 'for' is: 8 //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() 函数可实现在源字符串中搜索与指定字符（串）不相等的第 1 个字符。

find_last_not_of() 函数可实现在源字符串中搜索与指定字符（串）不相等的最后 1 个字符。

//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 << "find_first_of (): The position (forward) of 'P' is: " << (int) m << endl; cout << "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 << "find_first_of (): The position (forward) of 'some' is: " << (int) n << endl; cout << "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 << "find_first_of (): The position (forward) of 'drugs' is: " << (int) mo << endl; cout << "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 << "find_first_of (): The position of 'for' is: " << (int) no << endl; cout << "find_last_of () : The position of 'for' is: " << (int) rno << endl; cin.get (); return 0; } //程序运行结果为： //find_first_of (): The position (forward) of 'P' is: 0 //find_last_of (): The position (reverse) of 'P' is: 52 //find_first_of (): The position (forward) of 'some' is: 0 //find_last_of (): The position (reverse) of 'some' is: 52 //find_first_of (): The position (forward) of 'drugs' is: 0 //find_last_of (): The position (reverse) of 'drugs' is: 52 //find_first_of (): The position of 'for' is: 0 //find_last_of () : The position of 'for' is: 52