C++ 编程之std::string的utils

众所周知， C++标准库的std::string 如果用来处理字符串的话， 会很不友好，譬如使用字符串拆分split， 字符串数组组合啊， 字符串大小写转换之类的
本文讲述的是一些通过标准库现有接口实现的部分字符串操作方法

1. split

#include 

int count(const std::string& string, const std::string& sep)
{
    int cnt = 0;
    std::string::size_type index = string.find(sep, 0);
    while(index != std::string::npos) {
        ++cnt;
        index = string.find(sep, index + sep.size());
    }
    return cnt;
}

std::vector<std::string>  split(const std::string& string, const std::string& sep)
{
    std::vector<std::string> result;
    result.reserve(count(string, sep) + 1);
    std::string::size_type start = 0;
    std::string::size_type index = string.find(sep, start);
    while(index != std::string::npos) {
        result.push_back(string.substr(start, index - start));
        start = index + sep.size();
        index = string.find(sep, start);
    }
    result.push_back(string.substr(start));
    return result;
}

std::vector<std::string>  split_with_little_sep(const std::string& string, const std::string& sep)
{
    std::vector<std::string> result;
    std::string::size_type start = 0;
    std::string::size_type index = string.find(sep, start);
    while(index != std::string::npos) {
        result.push_back(string.substr(start, index - start));
        start = index + sep.size();
        index = string.find(sep, start);
    }
    result.push_back(string.substr(start));
    return result;
}

我这里写了两个版本, 从名字看， 第一种适合拆分分割的字符串出现次数比较多的情况， 第二种比较适合拆分分割字符串出现次数相当少或者没有的情况

2. join

#include 

std::string join(const std::string& s, const std::vector<std::string>& v)
{
    if(v.size() == 0) {
        return std::string();
    }
    auto size = v.size() - 1;
    std::ostringstream os;
    for(auto i = 0u; i < size; ++i) {
        os << v[i] << s;
    }
    os << v[size];
    return os.str();
}

3. upperCase/lowerCase

#include 
#include 
std::string lowerCase(const std::string& s)
{
    std::string result(s);
    std::transform(s.begin(), s.end(),
                   result.begin(),
                   [](unsigned char c) -> unsigned char { 
                       return std::tolower (c); 
                   } );
    return result;
}


std::string upperCase(const std::string& s)
{
    std::string result(s);
    std::transform(s.begin(), s.end(),
                   result.begin(),
                   [](unsigned char c) -> unsigned char {
                       return std::toupper (c);
                   } );
    return result;
}

4. replace

// source: 原字符串也是结果字符串
// olds: 要替换的部分
// news: 替换后的内容
// times： 替换次数， -1 表示全部替换
void replace_self(std::string& source, 
                    const std::string& olds, 
                    const std::string& news,
                    int times = -1)
{
    std::string::size_type index = source.find(olds);
    while(index != std::string::npos && times) {
        source.replace(index, olds.size(), news);
        index = source.find(olds);
        times = times > 0 ? times - 1 : times;
    }
}

std::string replace(const std::string& source, 
                    const std::string& olds, 
                    const std::string& news
                    int times = -1)
{
    std::string dest(source);
    replace_self(dest, olds, news, times);
    return dest;
}

5. startsWith/endsWith

bool startsWith(const std::string& source, const std::string& head)
{
    return head.size() <= source.size() 
            && source.compare(0, head.size(), head) == 0;
}

bool endsWith(const std::string& source, const std::string& tail)
{
    return tail.size() <= source.size() 
            && source.compare(source.size() - tail.size(), tail.size(), tail) == 0;
}

6. trim

    std::string trim(const std::string& source, const std::string& chars) {
        std::string other(source);
        auto start = other.find_first_of(chars);
        auto end = other.find_first_not_of(chars, start);
        while(start != npos) {
            other.erase(start, end - start);
            start = other.find_first_of(chars);
            end = other.find_first_not_of(chars, start);
        }
        return other;
    }

后续待更新……