string裡面的常用c函式 //2018/12/18-
string裡面的函式
(1)toupper函式
該函式把小寫字母變成大寫字母;
例項:
#include<iostream>
#include<string>
#include<cctype>
using namespace std;
int main()
{
char c = 'q';
c = toupper(c);
cout<<c;
}
//這個函式將cout<<Q;
(2)substr函式
用途:一種構造string的方法
形式:s.substr(pos, n)
解釋:返回一個string,包含s中從pos開始的n個字元的拷貝(pos的預設值是0,n的預設值是s.size() - pos,即不加引數會預設拷貝整個s)
補充:若pos的值超過了string的大小,則substr函式會丟擲一個out_of_range異常;若pos+n的值超過了string的大小,則substr會調整n的值,只拷貝到string的末尾
例項:
#include<string>
#include<iostream>
using namespace std;
int main()
{
string s("12345asdf");
string a = s.substr(0,5); //獲得字串s中從第0位開始的長度為5的字串
cout << a << endl;
}
(3)erase函式
erase函式的原型如下:
(1)string& erase ( size_t pos = 0, size_t n = npos );
(2)iterator erase ( iterator position );
(3)iterator erase ( iterator first, iterator last );
也就是說有三種用法:
(1)erase(pos,n); 刪除從pos開始的n個字元,比如erase(0,1)就是刪除第一個字元
(2)erase(position);刪除position處的一個字元(position是個string型別的迭代器)
(3)erase(first,last);刪除從first到last之間的字元(first和last都是迭代器)
下面是例子:
#include <iostream> #include <string> using namespace std; int main () { string str ("This is an example phrase."); string::iterator it; // 第(1)種用法 str.erase (10,8); cout << str << endl; // "This is an phrase." // 第(2)種用法 it=str.begin()+9; str.erase (it); cout << str << endl; // "This is a phrase." // 第(3)種用法 str.erase (str.begin()+5, str.end()-7); cout << str << endl; // "This phrase." return 0; }
(4)邏輯錯誤
int main()
{
string i="asd";
i[2]='\0';
i=i+'p';
cout<<i;//會輸出“asd p”,而不是輸出“asdp”
}
(5)C++刪除string最後一個字元的幾種方法
#include<iostream>
#include<string>
using namespace std;
int main()
{
string str;
str = "123456";
cout << str << endl;
//方法一:使用substr()
str = str.substr(0, str.length() - 1);
cout << str << endl;
//方法二:使用erase()
str.erase(str.end() - 1);
cout << str << endl;
//方法三:使用pop_back()
str.pop_back();
cout << str << endl;
return 0;
}
(6)to_string函式
函式原型:
string to_string (int val);
string to_string (long val);
string to_string (long long val);
string to_string (unsigned val);
string to_string (unsigned long val);
string to_string (unsigned long long val);
string to_string (float val);
string to_string (double val);
string to_string (long double val);
功能:
將數值轉化為字串。返回對應的字串。
示例:
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string pi = "pi is " + std::to_string(3.1415926);
string perfect = std::to_string(1+2+4+7+14) + " is a perfect number";
cout << pi << '\n';
cout << perfect << '\n';
return 0;
}
結果:
pi is 3.141593
28 is a perfect number
(7)insert()函式
#include <iostream>
#include <string>
int main (){
std::string str="to be question";
std::string str2="the ";
std::string str3="or not to be";
std::string::iterator it;
// used in the same order as described above:
str.insert(6,str2); // to be (the )question
str.insert(6,str3,3,4); // to be (not )the question
str.insert(10,"that is cool",8); // to be not (that is )the question
str.insert(10,"to be "); // to be not (to be )that is the question
str.insert(15,1,':'); //加一個'.' to be not to be(:) that is the question
it = str.insert(str.begin()+5,','); // to be(,) not to be: that is the question
str.insert (str.end(),3,'.'); // to be, not to be: that is the question(...)
str.insert (it+2,str3.begin(),str3.begin()+3); // (or )
std::cout << str << '\n';
return 0;
}
//output to be, or not to be: that is the question...
string的成員函式insert有以下多種過載:
string &insert(int p0, const char *s);——在p0位置插入字串s
string &insert(int p0, const char *s, int n);——在p0位置插入字串s的前n個字元
string &insert(int p0,const string &s);——在p0位置插入字串s
string &insert(int p0,const string &s, int pos, int n);——在p0位置插入字串s從pos開始的連續n個字元
string &insert(int p0, int n, char c);//在p0處插入n個字元c
iterator insert(iterator it, char c);//在it處插入字元c,返回插入後迭代器的位置
void insert(iterator it, const_iterator first, const_iteratorlast);//在it處插入從first開始至last-1的所有字元
void insert(iterator it, int n, char c);//在it處插入n個字元c