c++ string詳解 assign

assign方法可以理解為先將原字符串清空，然后賦予新的值作替換。

返回類型為 string類型的引用。其常用的重載也有下列幾種：

 

a. string& assign ( const string& str );

將str替換原字串的內容

舉例：

string testassign = "Hello World";

testassign.assign("Go home");

cout<<testassign<<endl;

//打印結果為 go home

 

b. string& assign ( const string& str, size_t pos, size_t n );

將str的內容從位置pos起的n個字符作為原字串的新內容賦給原字串

string testassign = "Hello World";

testassign.assign("Come on!", 5, 2);

cout<<testassign<<endl;

//打印結果為 on

 

c. string& assign ( const char* s, size_t n );

將字符數組或者字符串的首n個字符替換原字符串內容

舉例：

string testassign = "Hello World";

testassign.assign("go back to China", 7);

cout<<testassign<<endl;

//打印結果為go back

 

d. string& assign ( const char* s );

將字符串或者字符數組作為新內容替換原字串

舉例：

string testassign = "Hello World";

char ch[20] = "go back to shanghai";

testassign.assign(ch);

cout<<testassign<<endl;

//打印結果為 go back to shanghai

 

e. string& assign ( size_t n, char c );

將原字串替換為n個字符c

舉例：

string testassign = "Hello World";

char ch = '?';

testassign.assign(5, ch);

cout<<testassign<<endl;

//打印結果為?????

 

f. template <class InputIterator>   string& assign ( InputIterator first, InputIterator last );

需要include <iterator>

舉例：

string testassign = "Hello World";

testassign.assign(istream_iterator<char>(cin), istream_iterator<char>());

//輸入abcde

cout<<testassign<<endl;

//打印結果為 abcde

 

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string& assign ( const string& str );
string& assign ( const string& str, size_t pos, size_t n );
string& assign ( const char* s, size_t n );
string& assign ( const char* s );
string& assign ( size_t n, char c );
template <class InputIterator>
   string& assign ( InputIterator first, InputIterator last );

Assign content to string

Assigns new content to the string replacing its current content.

The arguments passed to the function determine the new content:

string& assign ( const string& str );

Sets a copy of  str as the new content.

string& assign ( const string& str, size_t pos, size_t n );

Sets a copy of a substring of  str as the new content. The substring is the portion of  str that begins at the character position  pos and takes up to  n characters (it takes less than  n if the end of  str is reached before).

string& assign ( const char * s, size_t n );

Sets as the new content a copy of the string formed by the first  n characters of the array pointed by  s.

string& assign ( const char * s );

Sets a copy of the string formed by the null-terminated character sequence (C string) pointed by  s as the new content. The length of the character sequence is determined by the first ocurrence of a null character (as determined by  traits.length(s)).

string& assign ( size_t n, char c );

Sets a string formed by a repetition of character  c,  n times, as the new content.

template<class InputIterator> string& assign (InputIterator first, InputIterator last);

If  InputIterator is an integral type, behaves as the previous member function version, effectively setting as the new content a string formed by the repetition  first times of the character equivalent to  last.
In any other case, the content is set to the values of the elements that go from element referred to by iterator  first to the element right before the one referred to by iterator  last.

 

Parameters

str

Another object of class  string whose content is entirely or partially copied as the new content for the string.

pos

Starting position of the substring of the  string object  str that forms the new content. Notice that the first position has a value of  0, not  1.
If the position passed is past the end of  str, an  out_of_range exception is thrown.

n

Number of characters to use for the content (i.e., its length).

s

Array with a sequence of characters.
In the third member function version, the length is determined by parameter  n, even including null characters in the content.
By contrast, in the fourth member version,  s is a null-terminated character, and therefore its length is determined only by the first occurrence of a null character.

c

Character value to be repeated  n times to form the new content.

start

If along with  last, both are integers, it is equivalent to parameter  n, otherwise it is an iterator referring to the beginning of a sequence of characters.

last

If along with  start, both are integers, it is equivalent to parameter  c, otherwise it is an iterator referring to the past-the-end element of a sequence of characters.

 

Return Value

*this

Example

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// string::assign #include <iostream> #include <string> using namespace std; int main () { string str; string base="The quick brown fox jumps over a lazy dog."; // used in the same order as described above: str.assign(base); cout << str << endl; str.assign(base,10,9); cout << str << endl; // "brown fox" str.assign("pangrams are cool",7); cout << str << endl; // "pangram" str.assign("c-string"); cout << str << endl; // "c-string" str.assign(10,'*'); cout << str << endl; // "**********" str.assign<int>(10,0x2D); cout << str << endl; // "----------" str.assign(base.begin()+16,base.end()-12); cout << str << endl; // "fox jumps over" return 0; }