C++【string】用法和例子

/***
 * string 基礎api複習
 * 8 AUG 2018
 */

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

void print(string str, int index)
{
    std::cout << "str" << index << " = " << str << std::endl;
}

int main()
{
    // string物件初始化
    string str0("i am a boy~");
    string str1 = "hello world!";
    string str2(str1);
    string str3(5, 'c');
    string str4(str1, 2, 3); // 從【2】索引起始，長度為3的字串

    print(str0, 0);
    print(str1, 1);
    print(str2, 2);
    print(str3, 3);
    print(str4, 4);

    // string相關簡單函式
    bool power;
    int str_len;
    char te_ch;
    string te_str;
    power = str0.empty();   // 判斷字串是否為空
    std::cout << "power = " << power << std::endl;
    str_len = str1.size();  // 字串長度
    std::cout << "str_len = " << str_len << std::endl;
    te_ch = str2[4];        // 返回字串的第n個字元，下標從0開始
    std::cout << "str2[4] = " << te_ch << std::endl;
    te_ch = str2.at(4);     // 返回字串的第n個字元，下標從0開始,同上
    std::cout << "str2.at(4) = " << te_ch << std::endl;
    te_str = str1 + str0;   // 連線兩個字串變成一個新的字串
    std::cout << "str1 + str0 = " << te_str << std::endl;
    te_str = str3;          // 替換字串
    std::cout << "te_str = " << te_str << std::endl;
    te_str.append(str0);    // 追加字串
    std::cout << "te_str = " << te_str << std::endl;
    te_str.assign(str0);    // 為字串物件賦值
    std::cout << "te_str = " << te_str << std::endl;

    // str.begin()&&str.end()均為迭代器
    string::iterator it = str0.begin();    // 字串迭代器，類似指標
    std::cout << "it = " << (*it) << std::endl;

    // string::c_str()
    char* char_str = new char[strlen(str0.c_str()) + 1];
    strcpy(char_str, str0.c_str());        // 當需要將字串轉成const char*時，用c_str(意味著轉換成C語音的方式)
    std::cout << "char_str = " << char_str << std::endl;
    delete []char_str;
    char_str = NULL;

    // string::erase()，注意，erase後迭代器自動指向後一個位置
    str0.erase(5, 2);                                // 從index值為5.刪除長度為4個字元
    std::cout << "str0.erase(5, 2) = " << str0 << std::endl;
    str0.erase(str0.begin() + 2);                    // 刪除index值為2的字元      
    std::cout << "str0.erase(str0.begin() + 2) = " << str0 << std::endl;
    str0.erase(str0.begin() + 2, str0.end() - 1);   // 從index值為2，刪除到index末尾減一
    std::cout << "str0.erase(str0.begin() + 2) = " << str0 << std::endl;

    // string::find()
    std::size_t found = str1.find(str4, 0);         // 從str1中找str4第一次出現的地方
    if (found != string::npos)
        std::cout << "first found is " << found << std::endl;
    found = str1.find('o');                         // 從str1中找o第一次出現的地方
    if (found != string::npos)
        std::cout << "first found is " << found << std::endl;
    found = str1.find("world");                     // 從str1中找world第一次出現的地方
    if (found != string::npos)
        std::cout << "first found is " << found << std::endl;    

    // string::insert()
    str0.insert(1, " love");        // 在str0的index值為1後插入 love
    print(str0, 0);
    str0.insert(6, " you", 0, 3);   // 在str0的index值為6後插入 you中從index值為0到長度為3的字串
    print(str0, 0);
    str0.insert(0, str1);           // 在str0的index值為0後插入str1
    print(str0, 0);

    // string::length()與string::size()用法相同，值也一樣
    std::cout << "str0.length() = " << str0.length() << " str0.size() = " << str0.size() << std::endl;

    // string::maxsize()返回能夠儲存字串的最大長度
    std::cout << "str0.max_size() = " << str0.max_size() << std::endl;

    // string::rbegin()和string::rend()逆向迭代器
    for (string::reverse_iterator it = str0.rbegin(); it != str0.rend(); it++)
    {
        std::cout << (*it);
    }
    std::cout << std::endl;
    print(str0, 0);

    // 這個是algorithm裡面的，混入是為了對比效果
    reverse(str0.begin(), str0.end()); 
    print(str0, 0);

    // string::replace()用法類似string::insert()
    str0.replace(5, 3, "ni hao", 2, 4);
    print(str0, 0);

    // string::substr()
    te_str = str0.substr(5, 3);
    std::cout << "te_str = " << te_str << std::endl;

    // string::swap()
    te_str.swap(str0);
    print(str0, 0);
    std::cout << "te_str = " << te_str << std::endl;

    while (true)
    {
        getchar();
    }
    return 0;
}