compare()是字符串类的公共成员函数。它将字符串对象(或子字符串)的值与其参数指定的字符序列进行比较。
compare()可以为每个字符串处理多个参数，以便可以通过其索引和长度指定一个子字符串。
返回类型： compare()返回一个整数值而不是一个布尔值。
字符串:: compare()的不同语法：
- 语法1：比较字符串* this和字符串str。
int string::compare (const string& str) const Returns: 0 : if both strings are equal. A value < 0 : if *this is shorter than str or, first character that doesn't match is smaller than str. A value > 0 : if *this is longer than str or, first character that doesn't match is greater// CPP code for demonstrating // string::compare (const string& str) const #includeusing namespace std; void compareOperation(string s1, string s2) { // returns a value < 0 (s1 is smaller then s2) if((s1.compare(s2)) < 0) cout << s1 << " is smaller than " << s2 << endl; // returns 0(s1, is being comapared to itself) if((s1.compare(s1)) == 0) cout << s1 << " is equal to " << s1 << endl; else cout << "Strings didn't match "; } // Driver Code int main() { string s1("Geeks"); string s2("forGeeks"); compareOperation(s1, s2); return 0; } 输出：
Geeks is smaller than forGeeks Geeks is equal to Geeks - 语法2：最多对字符串* this的len个字符进行比较，以索引idx和字符串str开头。
int string::compare (size_type idx, size_type len, const string& str) const Throws out_of_range if index > size().// CPP code to demonstrate // int string::compare (size_type idx, size_type len, // const string& str) const #includeusing namespace std; void compareOperation(string s1, string s2) { // Compares 5 characters from index number 3 of s2 with s1 if((s2.compare(3, 5, s1)) == 0) cout << "Here, "<< s1 << " are " << s2; else cout << "Strings didn't match "; } // Driver Code int main() { string s1("Geeks"); string s2("forGeeks"); compareOperation(s1, s2); return 0; } 输出：
Here, Geeks are forGeeks - 语法3：比较字符串*的len个字符(以索引idx开头)和字符串str的最大str_len个字符(以索引str_idx开头)。
int string::compare (size_type idx, size_type len, const string& str, size_type str_idx, size_type str_len) const Throws out_of_range if idx > size(). Throws out_of_range if str_idx > str.size().// CPP code to demonstrate // int string::compare (size_type idx, size_type len, const string& // str, size_type str_idx, size_type str_len) const #includeusing namespace std; void compareOperation(string s1, string s2) { // Compares 5 characters from index number 0 of s1 with // 5 characters from index 3 of s2 if((s1.compare(0, 5, s2, 3, 5)) == 0) cout << "Welcome to " << s1 << s2 << " World"; else cout << "Strings didn't match "; } // Driver Code int main() { string s1("Geeks"); string s2("forGeeks"); compareOperation(s1, s2); return 0; } 输出：
Welcome, to GeeksforGeeks World - 语法4：将字符串* this的字符与C字符串cstr的字符进行比较。
int string::compare (const char* cstr) const// CPP code to demonstrate // int string::compare (const char* cstr) const #includeusing namespace std; void compareOperation(string s1, string s2) { // returns < 0 (s1 < "GeeksforGeeks") if((s1.compare("GeeksforGeeks")) < 0) cout << s1 << " is smaller than string " << "GeeksforGeeks"; //returns 0 (s2 is "forgeeks") if((s2.compare("forGeeks")) == 0) cout << endl << s2 << " is equal to string " << s2; else cout << "Strings didn't match "; } // Driver Code int main() { string s1("Geeks"); string s2("forGeeks"); compareOperation(s1, s2); return 0; } 输出：
Geeks is smaller than string GeeksforGeeks forGeeks is equal to string forGeeks - 语法5：最多对字符串* this的len个字符进行比较，从索引idx开始与C字符串cstr的所有字符进行比较。
int string::compare (size_type idx, size_type len, const char* cstr) const请注意，cstr可能不是空指针(NULL)。
// CPP code to demonstrate // int string::compare (size_type idx, size_type len, // const char* cstr) const #includeusing namespace std; void compareOperation(string s1) { // Compares 5 characters from 0 index of s1 with "Geeks" if((s1.compare(0, 5, "Geeks")) == 0) cout << s1 << " are " << "awesome people"; else cout << "Strings didn't match "; } // Driver Code int main() { string s1("Geeks"); compareOperation(s1); return 0; } 输出：
Geeks are awesome people - 语法6：比较，顶多字符串的len字符*此，从与所述字符数组字符的字符chars_len索引IDX。
int string::compare (size_type idx, size_type len, const char* chars, size_type chars_len)const请注意，char必须至少具有chars_len个字符。字符可以具有任意值。因此，“ \ 0”没有特殊含义。
// CPP code to demonstrate // int string::compare (size_type idx, size_type len, // const char* chars, size_type chars_len)const #includeusing namespace std; void compareOperation(string s1, string s2) { // Compares 5 characters from 0 index of s1 with // 5 characters of string "Geeks" if((s1.compare(0, 5, "Geeks", 5)) == 0) cout << "This is " << s1 << s2 ; else cout << "Strings didn't match "; } // Driver Code int main() { string s1("Geeks"); string s2("forGeeks"); compareOperation(s1, s2); return 0; } 输出：
This is GeeksforGeeks
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