STL 常用

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void read_file(const std::string& path, std::string& out)
{
    std::ifstream fs(path, std::ios_base::binary);
    fs.seekg(0, std::ios_base::end);
    auto size = fs.tellg();
    fs.seekg(0);
    out.resize(static_cast<size_t>(size));
    fs.read(&out[0], size);
}

std::string file_extension(const std::string& path)
{
    std::smatch m;
    auto pat = std::regex("\\.([a-zA-Z0-9]+)$");
    if (std::regex_search(path, m, pat)) {
        return m[1].str();
    }
    return std::string();
}

#ifndef S_ISREG
#define S_ISREG(m)  (((m)&S_IFREG)==S_IFREG)
#endif
#ifndef S_ISDIR
#define S_ISDIR(m)  (((m)&S_IFDIR)==S_IFDIR)
#endif

bool is_file(const std::string& path)
{
    struct stat st;
    return stat(path.c_str(), &st) >= 0 && S_ISREG(st.st_mode);
}

bool is_dir(const std::string& path)
{
    struct stat st;
    return stat(path.c_str(), &st) >= 0 && S_ISDIR(st.st_mode);
}

template <class Fn>
void split(const char* b, const char* e, char d, Fn fn)
{
    int i = 0;
    int beg = 0;

    while (e ? (b + i != e) : (b[i] != '\0')) {
        if (b[i] == d) {
            fn(&b[beg], &b[i]);
            beg = i + 1;
        }
        i++;
    }

    if (i) {
        fn(&b[beg], &b[i]);
    }
}

bool is_valid_path(const std::string& path) {
    size_t level = 0;
    size_t i = 0;

    // Skip slash
    while (i < path.size() && path[i] == '/') {
        i++;
    }

    while (i < path.size()) {
        // Read component
        auto beg = i;
        while (i < path.size() && path[i] != '/') {
            i++;
        }

        auto len = i - beg;
        assert(len > 0);

        if (!path.compare(beg, len, ".")) {
            ;
        } else if (!path.compare(beg, len, "..")) {
            if (level == 0) {
                return false;
            }
            level--;
        } else {
            level++;
        }

        // Skip slash
        while (i < path.size() && path[i] == '/') {
            i++;
        }
    }

    return true;
}

bool is_hex(char c, int& v)
{
    if (0x20 <= c && isdigit(c)) {
        v = c - '0';
        return true;
    } else if ('A' <= c && c <= 'F') {
        v = c - 'A' + 10;
        return true;
    } else if ('a' <= c && c <= 'f') {
        v = c - 'a' + 10;
        return true;
    }
    return false;
}

inline std::string to_lower(const char* beg, const char* end)
{
    std::string out;
    auto it = beg;
    while (it != end) {
        out += ::tolower(*it);
        it++;
    }
    return out;
}