C++ string join and split util

stringutil.cpp

#include <string>
#include <vector>
#include <iostream>
#include <cassert>


/** splits str into vector of substrings, str is not changed */
std::vector<std::string> StringSplit(std::string str, const std::string delim)
{
    std::vector<std::string> res;
    size_t pos;
    while ((pos = str.find(delim)) != std::string::npos)
    {
        res.push_back(str.substr(0, pos));
        str.erase(0, pos + delim.length());
    }
    res.push_back(str);
    return res;
}


/** joins a vector of strings into a single string */
std::string StringJoin(const std::vector<std::string> &strs, const std::string delim)
{
    if (strs.size() == 0) return "";
    std::vector<char> res;
    for (int i = 0; i < strs.size()-1; ++i)
    {
        for (auto c: strs[i]) res.push_back(c);
        for (auto c: delim) res.push_back(c);
    }
    for (auto c: strs[strs.size()-1]) res.push_back(c);
    return std::string{res.begin(), res.end()};
}


int main()
{
    using SV = std::vector<std::string>;
    assert
        (StringSplit("", "+=+") == (SV{""}));
    assert
        (StringSplit("hello", "+=+") == (SV{"hello"}));
    assert
        (StringSplit("hello hewolli heilu  ", " ") == (SV{"hello", "hewolli", "heilu", "", ""}));
    assert
        (StringSplit("hello+=+hweolli+=+heilu+=+h", "+=+") == (SV{"hello", "hweolli", "heilu", "h"}));
    assert
        (StringSplit("hello+=+hweolli+=+heilu+=+h", "++") == (SV{"hello+=+hweolli+=+heilu+=+h"}));
    assert
        (StringSplit("+=+hello+=+", "+=+") == (SV{"", "hello", ""}));
    assert
        (StringJoin(static_cast<const SV&>(SV{}), " ") == "");
    assert
        (StringJoin(static_cast<const SV&>(SV{""}), " ") == "");
    assert
        (StringJoin(static_cast<const SV&>(SV{"hello"}), " ") == "hello");
    assert
        (StringJoin(static_cast<const SV&>(SV{"hello", "hewolli", "heilu"}), " ") == "hello hewolli heilu");
    assert
        (StringJoin(static_cast<const SV&>(SV{"hello", "hewolli", "heilu", "", ""}), " ") == "hello hewolli heilu  ");
    std::puts("all tests passed!");
}