Single method string formatter

Because I don't want to download an entire library for a single function (which I do understand, was made better than I made mine), I decided to implement my own string formatting function.

I am not very proud of it, as I find it pretty ugly and unreadable.
This is only a string formatter with string-only arguments.
Efficiency is not a concern for me.

#include<iostream>
#include<unordered_map>
#include<string>

using std::string;
string formatString(string format, const std::unordered_map<string, string>& args) {
    string ret;

    string::size_type bracketLoc;
    while((bracketLoc = format.find_first_of('{')) != string::npos) {
        // Handling the escape character.
        if(bracketLoc > 0 && format[bracketLoc - 1] == '\\') {
            ret += format.substr(0, bracketLoc + 1);
            format = format.substr(bracketLoc + 1);
            continue;
        }

        ret += format.substr(0, bracketLoc);
        format = format.substr(bracketLoc + 1);

        bracketLoc = format.find_first_of('}');
        string arg = format.substr(0, bracketLoc);
        format = format.substr(bracketLoc + 1);

        auto it = args.find(arg);
        if(it == args.end()) {
            ret += "(nil)";
        } else {
            ret += it->second;
        }
    }

    ret += format;

    return ret;
}

int main() {
    std::cout << formatString("Hello, {Name}! {WeatherType} weather, right?", {
        {"Name", "Midnightas"},
        {"Fruit", "Apple"}
    });

    return 0;
}

Compile with -std=c++11.
The above program will output Hello, Midnightas! (nil) weather, right?.