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字符串流

字符串
2023-09-11 14:22:44 时间

string

string类可用“=”赋值，用“==”等值比较，用加号做串联。

包含头文件<string>

string类支持cin方式和cout方式输入输出。

#include <iostream>
#include <string>

using namespace std;

int main() {
    string stuff;
    cin >> stuff;
    cout << stuff;
    return 0;
}

 

string类构造函数

string() 创建空的字符串
string(const char *s) 用C字符串创建string对象
string(const string &s) 用现有字符串创建新的字符串 
#include <iostream>
#include <string>

using namespace std;

int main() {
    string stuff("hello");
    string stuff1 = stuff;
    cout << stuff1 << endl;
    return 0;
}

 

string重载运算符

>> << = += + [] 关系运算符

 

#include <iostream>
#include <string>

using namespace std;

int main() {
    string s1("hello");
    string s2 = "beijing";
    if (s1 == s2)
        cout << s1[1];
    else
        cout << s2 + "china";
    return 0;
}

 

string常用方法

 

 

 

 

#include <iostream>
#include <string>

using namespace std;

int main() {
    string s1("aaaaaaaa");
    string s2("beijing");
    s1.append(s2);
    s1.append(s2, 2, 3);
    s1.append(2, 'A');
    s1.assign(s2);
    s1.assign(s2, 2, 3);
    cout << s2.at(2) << endl;
    cout << *s2.begin() << endl;
    cout << s2.capacity() << endl;
    cout << s2.size() << endl;
    cout << s1.compare(s2) << endl;
    cout << s2.compare(s1) << endl;
    cout << s2.empty() << endl;
    cout << *(s2.end() - 1) << endl;
    cout << s2.erase(2, 3) << endl;
    cout << s2 << endl;
    string s3 = "eij";
    cout << s2.find(s3) << endl;
    cout << s2.find('b') << endl;
    cout << s1.insert(2, "bb") << endl;
    cout << s2.substr(2, 3) << endl;
    s1.swap(s2);
    cout << s1;
    return 0;
}

 

字符串流的类型

sstream 基于 std::string 编写的，包含：

  • class istringstream;
  • class ostringstream;
  • class stringbuf;
  • class stringstream;

ostringstream::str() 返回 std::string 类型的字符串

 

strstream 基于C类型字符串char*编写的，包含：

  • class strstreambuf;
  • class istrstream;
  • class ostrstream;
  • class strstream;

ostrstream::str() 返回 char* 类型的字符串

#include <iostream>
#include <sstream>

using namespace std;

int main() {
    // istringstream istr;
    // istr.str("1 56.7");
    istringstream istr("1 56.7");  // 空格为字符串的内部分界
    cout << istr.str() << endl;
    int a;
    float b;
    istr >> a;
    cout << a << endl;
    istr >> b;
    cout << b << endl;
    return 0;
}

put()

#include <iostream>
#include <sstream>

using namespace std;

int main() {
    ostringstream ostr;
    ostr.put('d');
    ostr.put('e');
    ostr << "fg";
    string gstr = ostr.str();
    cout << gstr;
    return 0;
}

put() 或者左移操作符向ostr插入单个字符或字符串

 

str()

#include <iostream>
#include <sstream>

using namespace std;

int main() {
    ostringstream outstr;
    int price = 130;
    char* ps = " to C++";
    outstr << "Pay only$" << price << ps << endl;
    string msg = outstr.str();
    cout << msg << endl;
    return 0;
}

str() 成员函数将stringstream对象转换为string字符串

 

stringstream

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

int main() {
    stringstream stream;
    string result;
    int i = 1000;
    stream << i;
    stream >> result;
    cout << result << endl;
    return 0;
}

stringstream 通常是用来做数据转换的

 

clear()

#include <iostream>
#include <sstream>

using namespace std;

int main() {
    stringstream sstr;
    // int 转 string
    int a = 100;
    string str;
    sstr << a;
    sstr >> str;
    cout << str << endl;
    // string 转 char[]
    sstr.clear();
    string name = "beijing";
    char cname[200];
    sstr << name;
    sstr >> cname;
    cout << cname;
    return 0;
}

多次转换时须调用 stringstream 的成员函数 clear()

 

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

int main() {
    string s = "ab,cd,e,fg,h";
    int n = s.size();
    for (int i = 0; i < n; ++i) {
        if (s[i] == ',') s[i] = ' ';
    }
    istringstream out(s);
    string str;
    out >> str;  // 以空格作为字符串的内部分隔
    cout << str << endl;
    while (out >> str) {  // 读到文件末尾的时候会返回0
        cout << str << ' ';
    }
    cout << endl;
    return 0;
}

 

 

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