C++博客-MemoryGarden's Blog-随笔分类-STL

string::compare

memorygarden — Tue, 29 Dec 2009 18:11:00 GMT

1 int compare ( const string& str ) const;
2 int compare ( const char* s ) const;
3 int compare ( size_t pos1, size_t n1, const string& str ) const;
4 int compare ( size_t pos1, size_t n1, const char* s) const;
5 int compare ( size_t pos1, size_t n1, const string& str, size_t pos2, size_t n2 ) const;
6 int compare ( size_t pos1, size_t n1, const char* s, size_t n2) const;

Compares the content of this object (or a substring of it, known as compared (sub)string) to the content of a comparing string, which is formed according to the arguments passed.
The member function returns 0 if all the characters in the compared contents compare equal, a negative value if the first character that does not match compares to less in the object than in the comparing string, and a positive value in the opposite case.
Notice that for string objects, the result of a character comparison depends only on its character code (i.e., its ASCII code), so the result has some limited alphabetical or numerical ordering meaning.
For other basic_string class instantitations, the comparison depends on the specific traits::compare function, where traits is one of the class template parameters.
0 if the compared characters sequences are equal, otherwise a number different from 0 is returned, with its sign indicating whether the object is considered greater than the comparing string passed as parameter (positive sign), or smaller (negative sign).

1 // comparing apples with apples
2 #include <iostream>
3 #include <string>
4 using namespace std;
5
6 int main ()
7 {
8   string str1 ("green apple");
9   string str2 ("red apple");
10
11   if (str1.compare(str2) != 0)
12     cout << str1 << " is not " << str2 << "\n";
13
14   if (str1.compare(6,5,"apple") == 0)
15     cout << "still, " << str1 << " is an apple\n";
16
17   if (str2.compare(str2.size()-5,5,"apple") == 0)
18     cout << "and " << str2 << " is also an apple\n";
19
20   if (str1.compare(6,5,str2,4,5) == 0)
21     cout << "therefore, both are apples\n";
22
23   return 0;
24 }

memorygarden 2009-12-30 02:11 发表评论

string::clear

memorygarden — Tue, 29 Dec 2009 17:54:00 GMT

The string content is set to an empty string, erasing any previous content and thus leaving its size at 0 characters.

1 // string::clear
2 #include <iostream>
3 #include <string>
4 using namespace std;
5
6 int main ()
7 {
8   string str;
9   char c;
10   cout << "Please type some lines of text. Enter a period to finish:\n";
11   do {
12     c=cin.get();
13     str += c;
14     if (c=='\n')
15     {
16        cout << str;
17        str.clear();
18     }
19   } while (c!='.');
20   return 0;
21 }

memorygarden 2009-12-30 01:54 发表评论

string::capacity

memorygarden — Sun, 27 Dec 2009 18:21:00 GMT

string::capacity

Returns the size of the allocated storage space in the string object.

Notice that the capacity is not necessarily equal to the number of characters that conform the content of the string (this can be obtained with members size or length), but the capacity of the allocated space, which is either equal or greater than this content size.

Notice also that this capacity does not suppose a limit to the length of the string. If more space is required to accomodate content in the string object, the capacity is automatically expanded, or can even be explicitly modified by calling member reserve.

The real limit on the size a string object can reach is returned by member max_size.

size_t capacity ( ) const;

1 // comparing size, length, capacity and max_size
2 #include <iostream>
3 #include <string>
4 using namespace std;
5
6 int main ()
7 {
8   string str ("Test string");
9   cout << "size: " << str.size() << "\n";
10   cout << "length: " << str.length() << "\n";
11   cout << "capacity: " << str.capacity() << "\n";
12   cout << "max_size: " << str.max_size() << "\n";
13   return 0;
14 }

memorygarden 2009-12-28 02:21 发表评论

string::begin

memorygarden — Sun, 27 Dec 2009 18:00:00 GMT

string::begin

Returns an iterator referring to the first character in the string.

1 iterator begin();
2 const_iterator begin() const;

1 // string::begin and string::end
2 #include <iostream>
3 #include <string>
4 using namespace std;
5
6 int main ()
7 {
8   string str ("Test string");
9   string::iterator it;
10   for ( it=str.begin() ; it < str.end(); it++ )
11     cout << *it;
12   return 0;
13 }

memorygarden 2009-12-28 02:00 发表评论

string::at

memorygarden — Sun, 27 Dec 2009 17:52:00 GMT

string::at

This member function behaves as operator[] , except that at also performs a range check, throwing an exception of type out_of_range in case that pos is not an actual position in the string

和[]运算符不同的地方是当它接受一个非法的参数的时候,会抛出异常

1 const char& at ( size_t pos ) const;
2 char& at ( size_t pos );

1 // string::at
2 #include <iostream>
3 #include <string>
4 using namespace std;
5
6 int main ()
7 {
8   string str ("Test string");
9   int i;
10   for (i=0; i < str.length(); i++)
11   {
12     cout << str.at(i);
13   }
14   return 0;
15 }

memorygarden 2009-12-28 01:52 发表评论

string::assign

memorygarden — Sun, 27 Dec 2009 17:48:00 GMT

string::assign
Assigns new content to the string replacing its current content.

return *this

1 // string::assign
2 #include <iostream>
3 #include <string>
4 using namespace std;
5
6 int main ()
7 {
8   string str;
9   string base="The quick brown fox jumps over a lazy dog.";
10
11   // used in the same order as described above:
12
13   str.assign(base);
14   cout << str << endl;
15
16   str.assign(base,10,9);
17   cout << str << endl;         // "brown fox"
18
19   str.assign("pangrams are cool",7);
20   cout << str << endl;         // "pangram"
21
22   str.assign("c-string");
23   cout << str << endl;         // "c-string"
24
25   str.assign(10,'*');
26   cout << str << endl;         // "**********"
27
28   str.assign<int>(10,0x2D);
29   cout << str << endl;         // "----------"
30
31   str.assign(base.begin()+16,base.end()-12);
32   cout << str << endl;         // "fox jumps over"
33
34   return 0;
35 }

memorygarden 2009-12-28 01:48 发表评论

string::append

memorygarden — Sun, 27 Dec 2009 17:41:00 GMT

string::append 在调用的string后面追加

return *this

c plusplus 代码:

1 // appending to string
2 #include <iostream>
3 #include <string>
4 using namespace std;
5
6 int main ()
7 {
8   string str;
9   string str2="Writing ";
10   string str3="print 10 and then 5 more";
11
12   // used in the same order as described above:
13   str.append(str2);                       // "Writing "
14   str.append(str3,6,3);                   // "10 "
15   str.append("dots are cool",5);          // "dots "
16   str.append("here: ");                   // "here: "
17   str.append(10,'.');                     // "."
18   str.append(str3.begin()+8,str3.end());  // " and then 5 more"
19   str.append<int>(5,0x2E);                // ".."
20
21   cout << str << endl;
22   return 0;
23 }

memorygarden 2009-12-28 01:41 发表评论