C++-計算字符串中某個字符的數量、替換某個字符、提取某一段字符

計算字符數量：
計算字符數量這個很簡單，網上也有很多方法，這里只是簡單記錄

方法：
int markNumber = count(str.begin(), str.end(), 'A');

替換某個字符：

方法：

    string str = "ABCDEAAA";
    string Character = "A";
    string replaceCharacter = "Q";

    int markNumber = count(str.begin(), str.end(), 'A');//計算字符數量
    cout << "A的數量為：" << markNumber << endl;
    cout << "替換前：" << str << endl;

    int pos = -1;
    pos = str.find(Character);
    while (-1 != pos)
    {
        str.replace(pos, string(Character).length(), replaceCharacter);
        pos = str.find(Character);
    }

    cout << "替換后：" << str << endl;

結果：

查找某一段字符：

方法：

    std::string str = "ABCD_EAAA";
    std::string underLine = "_";

    std::cout << "查找前：" << str << std::endl;

    int pos = -1;
    pos = str.find(underLine);
    std::string firstHalfCharacter = str.substr(0,pos);//注意：這里的0表示從第幾個字符開始，pos表示往后幾位
    std::string secondHalfCharacter = str.substr(pos+1,str.length());

    std::cout << "符號前的值：" << firstHalfCharacter << std::endl;//輸出值為"ABCD"
    std::cout << "符號后的值：" << secondHalfCharacter << std::endl;//輸出值為"EAAA"

    std::string str1 = "ABCDEFG";
    int pos1 = -1;
    pos1 = str1.find('C');
    int pos2 = -1;
    pos2 = str1.find('F');

    std::string character = str1.substr(pos1,pos2-pos1);
    std::cout << "中間某一段字符值：" << character << std::endl;//輸出值為"CDE"