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C++ 字符串類

2018-03-24 11:29 更新

學(xué)習(xí)C++ - C++字符串類

C++有一個字符串類。

您可以使用類型字符串變量。

要使用字符串類，程序必須包括字符串頭文件。

字符串類是std命名空間的一部分。

該類可以讓您將字符串視為普通變量。

例子

以下代碼說明了字符串對象和字符數(shù)組之間的一些相似之處和差異。


#include <iostream> 
#include <string>               // make string class available 
using namespace std; 
int main() { 
    char my_char1[20];            // create an empty array 
    char my_char2[20] = "C++"; // create an initialized array 
    string str1;                // create an empty string object 
    string str2 = "Java";    // create an initialized string 

    cout << "Enter a string: "; 
    cin >> my_char1; 
    cout << "Enter another string: "; 
    cin >> str1;                // use cin for input 
    cout << my_char1 << " " << my_char2 << " " 
          << str1 << " " << str2 // use cout for output 
          << endl; 
    cout << "The third letter in " << my_char2 << " is " 
          << my_char2[2] << endl; 
    cout << "The third letter in " << str2 << " is " 
          << str2[2] << endl;    // use array notation 

    return 0; 
}

上面的代碼生成以下結(jié)果。

例2

以下代碼顯示了一些String用法。

請注意，您可以將C風(fēng)格的字符串以及字符串對象添加到字符串對象。


#include <iostream> 
#include <string>               // make string class available 
using namespace std; 
int main() { 
    string s1 = "www.15014759268.cn"; 
    string s2, s3; 

    cout << "You can assign one string object to another: s2 = s1\n"; 
    s2 = s1; 
    cout << "s1: " << s1 << ", s2: " << s2 << endl; 
    cout << "You can assign a C-style string to a string object.\n"; 
    cout << "s2 = \"new Value\"\n"; 
    s2 = "C++"; 
    cout << "s2: " << s2 << endl; 
    cout << "You can concatenate strings: s3 = s1 + s2\n"; 
    s3 = s1 + s2; 
    cout << "s3: " << s3 << endl; 
    cout << "You can append strings.\n"; 
    s1 += s2; 
    cout <<"s1 += s2 yields s1 = " << s1 << endl; 
    s2 += " for a day"; 
    cout <<"s2 += \" for a day\" yields s2 = " << s2 << endl; 

    return 0; 
}

上面的代碼生成以下結(jié)果。

例3

C庫相當(dāng)于

str3 = str1 + str2;

這是:

strcpy(my_char3, my_char1); 
strcat(my_char3, my_char2);

以下代碼將使用字符串對象的技術(shù)與使用字符數(shù)組的技術(shù)進(jìn)行比較。


#include <iostream> 
#include <string>               // make string class available 
#include <cstring>              // C-style string library 
using namespace std; 
int main() { 
     char my_char1[20]; 
     char my_char2[20] = "www.15014759268.cn"; 
     string str1; 
     string str2 = "C++"; 

     str1 = str2;                // copy str2 to str1 
     strcpy(my_char1, my_char2); // copy my_char2 to my_char1 

     str1 += " vs ";              // add to the end of str1 
     strcat(my_char1, " Java");   // add to the end of my_char1 

     int len1 = str1.size();     // obtain length of str1 
     int len2 = strlen(my_char1);// obtain length of my_char1 

     cout << "The string " << str1 << " contains " 
           << len1 << " characters.\n"; 
     cout << "The string " << my_char1 << " contains " 
           << len2 << " characters.\n"; 

     return 0; 
}

上面的代碼生成以下結(jié)果。

字符串類I/O

您可以使用cin與>>操作符來讀取一個字符串對象，并使用<<操作符來顯示一個使用與C風(fēng)格字符串相同的語法的字符串對象。

一次讀取一行而不是一個字使用不同的語法。


#include <iostream> 
#include <string>               // make string class available 
#include <cstring>              // C-style string library 
using namespace std; 
int main() { 
     char my_char[20]; 
     string str; 

     cout << "Length of string: " 
          << strlen(my_char) << endl; 
     cout << "Length of string in str before input: " 
          << str.size() << endl; 
     cout << "Enter a line of text:\n"; 
     cin.getline(my_char, 20);     // indicate maximum length 
     cout << "You entered: " << my_char << endl; 
     cout << "Enter another line of text:\n"; 
     getline(cin, str);          // cin now an argument; no length specifier 
     cout << "You entered: " << str << endl; 
     cout << "Length of string in my_char after input: " 
          << strlen(my_char) << endl; 
     cout << "Length of string in str after input: " 
          << str.size() << endl; 
     return 0; 
}

上面的代碼生成以下結(jié)果。