【C++】文字列中に指定文字列がいくつ出現するかカウントする関数。UTF-8の文字列の長さを取得する関数。

cpp_string_count_test.cpp

#include <iostream>

/**
 *  @brief  Return the number of occurrences of substring 'sub in string 'src'.
 *  @param  src search target.
 *  @param  sub substring.
 *  @return the number of occurrences of substring.
 */
int countSubStr(std::string &src, std::string &sub)
{
    size_t len = src.length();
    int count = 0;
    for(int idx = 0; idx < len; ++count) {
        int ret = src.find(sub, idx);
        if(ret == std::string::npos)
            break;
        idx = ret + 1;
    }
    return count;
}

/**
 *  @brief  Return the length of UTF-8 String.
 *  @param  str UTF-8 String.
 *  @return the length of UTF-8 String.
 */
int getLengthUTF8String(const char *str)
{
    // Note: http://ja.wikipedia.org/wiki/UTF-8
    //
    //  1byte: 0xxxxxxx
    //  2byte: 110xxxxx
    //  3byte: 1110xxxx
    //  4byte: 11110xxx
    constexpr const int kBitChecker[] {
        0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80
    };

    int count = 0, idx = 0;
    char ch;
    while((ch = str[idx]) != '\0') {
        // 1 byte characters
        if(!(ch & kBitChecker[8])) {
            count++;
            idx++;

        // 2 byte characters
        } else if((ch & kBitChecker[8]) && (ch & kBitChecker[7]) && !(ch & kBitChecker[6])) {
            count++;
            idx += 2;

        // 3 byte characters
        } else if((ch & kBitChecker[8]) && (ch & kBitChecker[7]) &&
                (ch & kBitChecker[6]) && !(ch & kBitChecker[5])) {
            count++;
            idx += 3;

        // 4 byte characters
        } else if((ch & kBitChecker[8]) && (ch & kBitChecker[7]) &&
                (ch & kBitChecker[6]) && (ch & kBitChecker[5]) && !(ch & kBitChecker[4])) {
            count++;
            idx += 4;

        // Is not first character
        } else {
            idx++;
            continue;
        }
    }
    return count;
}
int getLengthUTF8String(std::string &str) {
    return getLengthUTF8String(str.c_str());
}

int main(int argc, const char **argv)
{
    std::string src, sub;
    if(argc >= 3) {
        src = argv[1];
        sub = argv[2];
    } else {
        src = "abcabcabc";
        sub = "bc";
    }

    std::cout << "src = " << src << std::endl;
    std::cout << "sub = " << sub << std::endl;

    // Test.
    int cnt = countSubStr(src, sub);
    std::cout << "cnt = " << cnt << std::endl;

    // Test2.
    std::cout << "------------------------" << std::endl;
    std::string utf8 = "ABCDEΑΒΓΔΕあいうえお𥼣𥽜𥿠𥿔𨷻";
    int len = getLengthUTF8String(utf8);
    std::cout << "utf8 = " << utf8 << std::endl;
    std::cout << "length = " << utf8.length() << std::endl;
    std::cout << "getLengthUTF8String = " << len << std::endl;
    return 0;
}