C++标准库string学习笔记

string概述

作为c++语言用作字符串处理的标准库，和Python字符串类型有较多相似之处。可以使用‘=’进行赋值，“==”来比较，“+”进行拼接。

构造函数

• string s;直接声明变量
• string s(str);创建一个str的副本s
• string s(str,idx)；将str字符串索引值及其后面的部分当做s初值
• string s(str,idx,len);将str从idx开始，长度为len的内容赋值给s
• string s(c-str);将char*字符串作为字符串s初值
• string s(chars,len);以字符数组的前len个元素作为s初值
• string s(num,c);生成num个c字符的字符串。c为int类型
• string s(begin,end);将[begin， end]区间内的字符做为s初值,begin,end为可迭代对象
• string s(init-list);将init-list内字符做为s初值

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示例代码

点击查看代码

#include <iostream>
#include <string>
#include <cstring>
using namespace std;

int main() {
    /*构造字符串*/
    string str1="hello world";
    cout<<"str1:"<<str1<<endl;
    string str2(str1);
    cout<<"str2:"<<str2<<endl;
    string str3(str1,2);
    cout<<"str3:"<<str3<<endl;
    string str4(str1,2,3);
    cout<<"str4:"<<str4<<endl;
    char word[20]="new string";
    string str5(word,5);
    cout<<"str5:"<<str5<<endl;
    string str6(word);
    cout<<"str6:"<<str6<<endl;
    string str7(&str6[2],&str6[7]);
    cout<<"str7:"<<str7<<endl;
    char *a="c-----string";
    string str8(a,5);
    cout<<"str8:"<<str8<<endl;
    string str9(a);
    cout<<"str9:"<<str9<<endl;
    string str10(10,121);
    cout<<"str10:"<<str10<<endl;
    return 0;
}

输出结果为：

----------------------------------------
					str1:hello world
					str2:hello world
					str3:llo world
					str4:llo
					str5:new s
					str6:new string
					str7:w str
					str8:c----
					str9:c-----string
					str10:yyyyyyyyyy

					进程已结束，退出代码为 0
--------------------------------------------------

string值操作

• =,assign(str);直接赋值，相互等价
• swap(str1,str2);将str1与str2值交换
• +，append(str)；字符串拼接
• push_back(c);c为int类型
• pop_back();移除末尾字符
• insert(pos,str);指定pos处添加str
• erase(i);保留前i位字符，i<=str.size()
• resize(len);保留前len位字符,长度不够则补位；

示例代码

点击查看代码

#include <iostream>
#include <string>
#include <cstring>

using namespace std;

int main() {
    string str1="hello world";
    cout<<"str1:"<<str1<<endl;
    /*赋值操作*/
    str1="你好";
    cout<<"str1:"<<str1<<endl;
    str1.assign("a new string!");
    cout<<"str1:"<<str1<<endl;
    string str2;
    str2.assign("1234567");
    cout<<"str2:"<<str2<<endl;
    swap(str1,str2);
    cout<<"str1:"<<str1<<endl;
    cout<<"str2:"<<str2<<endl;
    str2.append(",ok");
    cout<<"str2:"<<str2<<endl;
    str1+="10";
    cout<<"str1:"<<str1<<endl;
    str1.push_back('1');
    cout<<"str1:"<<str1<<endl;
    str1.pop_back();
    cout<<"str1:"<<str1<<endl;
    str2.insert(3,"insert data");
    cout<<"str2:"<<str2<<endl;
    str2.erase(22);
    cout<<"str2:"<<str2<<endl;
    cout<<"str2大小:"<<str2.size()<<endl;
    str1.resize(16);
    cout<<"str1:"<<str1<<endl;
}

输出结果为：

----------------------------------------
				str1:hello world
				str1:你好
				str1:a new string!
				str2:1234567
				str1:1234567
				str2:a new string!
				str2:a new string!,ok
				str1:123456710
				str1:1234567101
				str1:123456710
				str2:a ninsert dataew string!,ok
				str2:a ninsert dataew strin
				str2大小:22
				str1:123456710

进程已结束，退出代码为 0

--------------------------------------------------

替换字符str.replace()

• str.replace(pos,n,str2);将str 从[pos]开始的n个元素用str2替代；
• str.replace(pos1,n1,str2,pos2,n2);将str 从[pos1]开始的n1个元素用str2从[pos2]开始的n2个元素替代；
• str.replace(i1,i2,k1,k2);将i1-i2元素用k1-k2元素代替，i1,i2,k1,k2均为可迭代对象

点击查看代码

#include <iostream>
#include <string>

using namespace std;

int main() {
    string str3 = "0123456780000";
    string str4 = "asdfghjkl@#$";
    cout << "str3:" << str3 << endl;
    cout << "str4:" << str4 << endl;
    str4.replace(5, 5, str3);
    cout << "str4:" << str4 << endl;
    str4.replace(0, 7, str3, str3.find("2"), 4);
    cout << "str4:" << str4 << endl;
    str4.replace(str4.begin() + 3, str4.begin() + 5, str3.begin(), str3.end() - 3);
    cout << "str4:" << str4 << endl;
}

输出结果：
	--------------------------------------
					str3:0123456780000
					str4:asdfghjkl@#$
					str4:asdfg0123456780000#$
					str4:234523456780000#$
					str4:23401234567803456780000#$
					进程已结束，退出代码为 0
	---------------------------------------

字符串与数字相互转换

字符串转数字

• stoi();转换为int型
• stol();转换为long int型
• stoll();转换为long long 型
• stoul();转换为 unsigned long型
• stoull();转换为unsigned long long 型
• stof();转换为float型
• stod();转换为double型
• stold();转换为long double型
• to_string();将数字转换为string；

点击查看代码

#include <iostream>
#include <string>

using namespace std;

int main() {
    string str1 = "-12345";
    string str2 = "-345.78888";
    auto num1 = stoi(str1);
    auto num2 = stol(str1);
    auto num3 = stold(str1);
    cout << "num1=" << num1 << endl;
    cout << "num2=" << num2 << endl;
    cout << "num3=" << num3 << endl;
    string str3 = "12345";
    auto num4 = stoul(str3);
    auto num5 = stoull(str3);
    cout << "num4=" << num4 << endl;
    cout << "num5=" << num5 << endl;
    auto num6 = stof(str2);
    auto num7 = stod(str2);
    auto num8 = stold(str2);
    cout << "num6=" << num6 << endl;
    cout << "num7=" << num7 << endl;
    cout << "num8=" << num8 << endl;
    auto num10=-12.3456;
    auto str4= to_string(num10);
    cout << "num10->str:" << str4 << endl;
}

输出结果
----------------------------------
					num1=-12345
					num2=-12345
					num3=-12345
					num4=12345
					num5=12345
					num6=-345.789
					num7=-345.789
					num8=-345.789
                                            num10->str:-12.345600
					进程已结束，退出代码为 0
------------------------------------------------
***不可将“-123"转换为unsigned 型，不可将“123.12”转换为int型,可以将“-1234”转换为浮点类型***

字符搜索和查找

• find()
• rfind()
• find_first_of()
• find_last_of()
• find_first_not_of()
• find_last_not_of()
  
  实参(value,pos,n):
  
  value:要查找的字符值
  
  pos,开始查找的位置
  
  n，查找范围
  
  返回值，索引

示例代码

点击查看代码

#include <iostream>
#include <string>

using namespace std;

int main() {
    string str1 = "In addition, some swarm intelligence methods that mimic\n "
                  "biological behaviors are also gradually applied to regional\n"
                  "coverage planning tasks. Reference proposed a rule-\n"
                  "based collaborative search algorithm based on the kinetic\n"
                  "model-Boids.";
    cout<<str1.size()<<endl;
    string str2(str1,100,10);
    cout<<str2<<endl;
    cout<<str1.find_first_of("t",100,100);
}

输出结果：
-------------------------------------
					244
					lied to re
					104
					进程已结束，退出代码为 0
-----------------------------------------------