成员函数assign()用于分配，它为字符串分配一个新值，以替换其当前内容。语法1：分配字符串str的值。
string& string::assign (const string& str) str: is the string to be assigned. 返回： *this
// CPP code for assign (const string& str)
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate assign
void assignDemo(string str1, string str2)
{
// Assigns str2 to str1
str1.assign(str2);
cout << "After assign():";
cout << str1;
}
// Driver code
int main()
{
string str1("Hello World!");
string str2("GeeksforGeeks");
cout << "Original String:" << str1 << endl;
assignDemo(str1, str2);
return 0;
}输出：
Original String:Hello World! After assign():GeeksforGeeks
语法2：从索引str_idx开始分配最多str的str_num个字符。如果str_idx> str，则抛出_range _range。 size()。
string& string::assign (const string& str, size_type str_idx, size_type str_num) str: is the string to be assigned. str_idx:is the index number in str. str_num:is the number of characters picked from str_idx to assign 返回： *this
// CPP code to illustrate
// assign(const string& str, size_type str_idx, size_type str_num)
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate assign
void assignDemo(string str1, string str2)
{
// Assigns 13 charaacters from
// 5th index of str2 to str1
str1.assign(str2, 5, 13);
cout << "After assign():";
cout << str1;
}
// Driver code
int main()
{
string str1("Hello World!");
string str2("GeeksforGeeks");
cout << "Original String:" << str1 << endl;
assignDemo(str1, str2);
return 0;
}输出：
Original String:Hello World! After assign():forGeeks
语法3：分配C-string cstr的字符。如果结果大小超过最大字符数，它将抛出length_error。
string & string::assign (const char* cstr) Assigns all characters of cstr up to but not including '\0'. 返回： *this. Note: that cstr may not be a null pointer (NULL).
// CPP code for assign (const char* cstr)
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate assign
void assignDemo(string str)
{
// Assigns GeeksforGeeks to str
str.assign("GeeksforGeeks");
cout << "After assign():";
cout << str;
}
// Driver code
int main()
{
string str("Hello World!");
cout << "Original String:" << str << endl;
assignDemo(str);
return 0;
}输出：
Original String:Hello World! After assign():GeeksforGeeks
语法4：分配字符数组chars的chars_len字符。如果结果大小超过最大字符数，它将抛出length_error。
string& string::assign (const char* chars, size_type chars_len) *chars: is the pointer to the array to be assigned. chars_len:is the number of characters to be assigned from character array. Note: that chars must have at least chars_len characters. 返回： *this.
// CPP code to illustrate
// string& string::assign (const char* chars, size_type chars_len)
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate assign
void assignDemo(string str)
{
// Assigns first 5 characters of
// GeeksforGeeks to str
str.assign("GeeksforGeeks", 5);
cout << "After assign():";
cout << str;
}
// Driver code
int main()
{
string str("Hello World!");
cout << "Original String:" << str << endl;
assignDemo(str);
return 0;
}输出：
Original String:Hello World! After assign():Geeks
Synatx 5：分配字符c的出现次数。如果num等于string::npos，则抛出length_error
string & string::assign (size_type num, char c) num: is the number of occurrences to be assigned. c: is the character which is to be assigned repeatedly. Throws length_error if the resulting size exceeds the maximum number(max_size) of characters. 返回： *this.
// CPP code for string& string::assign (size_type num, char c)
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate assign
void assignDemo(string str)
{
// Assigns 10 occurrences of 'x'
// to str
str.assign(10, 'x');
cout << "After assign():";
cout << str;
}
// Driver code
int main()
{
string str("#########");
cout << "Original String:" << str << endl;
assignDemo(str);
return 0;
}输出：
Original String:######### After assign():xxxxxxxxxx
语法6：分配范围[beg，end)的所有字符。如果范围超出了字符串的实际内容，它将引发length_error。
template <class InputIterator> string& assign (InputIterator first, InputIterator last) first, last:Input iterators to the initial and final positions in a sequence. 返回： *this.
// CPP code for string& string::assign (size_type num, char c)
#include <iostream>
#include <string>
using namespace std;
// Function to demonstrate assign
void assignDemo(string str)
{
string str1;
// Assigns all characters between
// str.begin()+6 and str.end()-0 to str1
str1.assign(str.begin()+6, str.end()-0);
cout << "After assign():";
cout << str1;
}
// Driver code
int main()
{
string str("Hello World!");
cout << "Original String:" << str << endl;
assignDemo(str);
return 0;
}输出：
Original String:Hello World! After assign():World!
相关用法
注：本文由纯净天空筛选整理自 std::string::assign() in C++。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。