C++學習（九）入門篇——String類

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可以用string類而不是字元數組來儲存字串，string更加簡單

要是用string類，則要在程式中包含標頭檔string，且位於std名稱空間中，string類隱藏了字串的數組性質，可以像處理普通變數那樣處理字串

程式清單4.7  strtype1.cpp//strtypel.cpp - - using the C++ string class#include<iostream>#include<string>int main(){    using namespace std;    char charr1[20];    char charr2[20] = "jaguar";    string str1;    string str2 = "panther";    cout << "Enter a kind of feline: ";    cin >> charr1;    cout << "Enter another kind of feline: ";    cin >> str1;    cin.get();    cout << "Here are some felines:\n";    cout << charr1 << " " << charr2 << " "        << str1 << " " << str2 << endl;    cout << "The third letter in " << charr2 << " is "        << charr2[2] << endl;    cout << "The third letter in " << str2 << " is "        << str2[2] << endl;    cin.get();}

輸出結果：

string對象聲明為簡單變數

char數組為一組用於儲存字串的char儲存單元，string類為一個儲存字串的實體

除了數組初始化可用列表初始化，也適用於字串初始化

char first_date[ ] ={"Le Chapon Dodu"};

string second_date={"Le Chapon Dodu"};

char third_date[ ] {"Le Chapon Dodu"};

string forth_date {"Le Chapon Dodu"};

 

不能將一個數組賦給另一個數組，但可以將一個string對象賦給另一個string對象

char charr1[20];char charr2[20] = "jaguar";string str1;string str2 = "panther";charr1=charr2;                      //不允許這麼做str1=str2;                             //可以

string類簡化了字串合併作業

還可以將兩個string對象合并起來

string str3;str3 = str1+str2;str1+=str2;

程式清單4.8 strtype2.cpp//strtype2.cpp - - assigning,adding,and appending#include<iostream>#include<string>int main(){    using namespace std;    string s1 = "penguin";    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 = \"buzzard\"\n";    s2 = "buzzard";    cout << "s2: " << s2 << endl;    cout << "You can concatenate strings:s3 = s2 + s1\n";    s3 = s2 + s1;    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;    cin.get();}

結果：

在C++新增string類前，還是要完成給字串賦值，用標頭檔cstring中的函數來完成，用函數strcpy（）將字串複製到字元數組中，用strcat（）將字串附加到字元數組末尾

strcpy(charr1,charr2);    //copy charr2 to charr1strcat(charr1,charr2);    //append contents of charr2 to charr1

程式清單4.9  strtype3.cpp//strtype3.cpp - - more string class features#include<iostream>#include<string>#include<cstring>int main(){    using namespace std;    char charr1[20];    char charr2[20] = "jaguar";    string str1;    string str2 = "panther";    str1 = str2;    strcpy_s(charr1,charr2);    str1 += " paste";    strcat_s(charr1, " juice");    int len1 = str1.size();    int len2 = strlen(charr1);    cout << "The string " << str1 << " contains "        << len1 << " characters.\n";    cout << "The string " << charr1 << " contains "        << len2 << " characters.\n";    cin.get();}

輸出：

函數strlen（）是一個常規函數，返回該字串包含的字元數。

str1是一個對象，而size（）是一個類對象，所以這樣調用str1.size（）

 

C++學習（九）入門篇——String類