C++-计算字符串中某个字符的数量、替换某个字符、提取某一段字符

计算字符数量：
计算字符数量这个很简单，网上也有很多方法，这里只是简单记录

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

替换某个字符：

方法：

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

    int markNumber = count(str.begin(), str.end(), 'A');//计算字符数量
    cout << "A的数量为：" << markNumber << endl;
    cout << "替换前：" << str << endl;

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

    cout << "替换后：" << str << endl;

结果：

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：这里的0表示从第几个字符开始，pos表示往后几位
    std::string secondHalfCharacter = str.substr(pos+1,str.length());

    std::cout << "符号前的值：" << firstHalfCharacter << std::endl;//输出值为"ABCD"
    std::cout << "符号后的值：" << secondHalfCharacter << std::endl;//输出值为"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 << "中间某一段字符值：" << character << std::endl;//输出值为"CDE"