call the appropriate function with arguments based on key received - c++

Question

In my application I'm calling different functions based on the message key received via network. But my implementation isn't that effective as it consists of exhaustive search for the key in the std::vector<std::string>. I'm thinking of using std::unordered_map<std::string, <fun>> but don't know how to map it to a function and also call that function by passing the required arguments. This is my current implementation:
#include <iostream>
#include <string>
#include <vector>
int main() {
std::vector<std::string> msg_key_list;
msg_key_list.emplace_back("key1");
msg_key_list.emplace_back("key2");
msg_key_list.emplace_back("key3");
msg_key_list.emplace_back("key4");
msg_key_list.emplace_back("key5");
char buff[2048];
ssize_t data_len;
while (true) {
// receive data from network
std::string msg(buff, data_len);
std::string::size_type pos = msg.find_first_of(",");
std::string key = msg.substr(0, pos - 1);
if (key == msg_key_list.at(0)) {
// validate the message received
bool valid;
if (!valid) {
std::cerr << "Invalid data: ";
std::cerr << __FILE__ << ", " << __PRETTY_FUNCTION__ << ", " << __LINE__ << "\n";
continue;
}
std::string val(buff + pos, msg.size() - pos);
// fun1(val);
} else if (key == msg_key_list.at(1)) {
// validate the message received
bool valid;
if (!valid) {
std::cerr << "Invalid data: ";
std::cerr << __FILE__ << ", " << __PRETTY_FUNCTION__ << ", " << __LINE__ << "\n";
continue;
}
std::string val(buff + pos, msg.size() - pos);
// fun2(val);
} else if (key == msg_key_list.at(2)) {
// validate the message received
bool valid;
if (!valid) {
std::cerr << "Invalid data: ";
std::cerr << __FILE__ << ", " << __PRETTY_FUNCTION__ << ", " << __LINE__ << "\n";
continue;
}
std::string val(buff + pos, msg.size() - pos);
// fun3(val);
} else if (key == msg_key_list.at(3)) {
// validate the message received
bool valid;
if (!valid) {
std::cerr << "Invalid data: ";
std::cerr << __FILE__ << ", " << __PRETTY_FUNCTION__ << ", " << __LINE__ << "\n";
continue;
}
std::string val(buff + pos, msg.size() - pos);
// fun4(val);
} else if (key == msg_key_list.at(4)) {
// validate the message received
bool valid;
if (!valid) {
std::cerr << "Invalid data: ";
std::cerr << __FILE__ << ", " << __PRETTY_FUNCTION__ << ", " << __LINE__ << "\n";
continue;
}
std::string val(buff + pos, msg.size() - pos);
// fun5(val);
}
}
}

Answer 1

I made an example of how I whould approach this (if all handlers would share the same function signature). I also avoid the string copying in the message handler because that would slow things done unecessarily.
#include <iostream>
#include <stdexcept>
#include <vector>
#include <map>
#include <string>
//-----------------------------------------------------------------------------
// function signature of your message handlers
using handler_t = void(*)(const std::string_view&);
//-----------------------------------------------------------------------------
// handler functions
void handler_1(const std::string_view& msg)
{
// validate data here
std::cout << "handler 1 : " << msg << std::endl;
};
void handler_2(const std::string_view& msg)
{
std::cout << "handler 2 : " << msg << std::endl;
};
//-----------------------------------------------------------------------------
// handler selection
void handle_message(const std::string& buffer)
{
static const std::map<std::string_view, handler_t> handler_map
{
{"key1",handler_1},
{"key2",handler_2}
};
try
{
// find location of first ',' (if any)
// also ensure the ',' is not too far back for splitting
auto index = buffer.find_first_of(',');
if ((index != std::string::npos) && (index < (buffer.length() - 1)))
{
auto pos = buffer.begin() + index;
// No need to copy data to seperate strings
// string_views will do.
std::string_view key{ buffer.begin(), pos };
std::string_view data{ pos + 1, buffer.end() };
// lookup handler, not if no handler is found
// a std::out_of_range exception will be thrown
auto handler = handler_map.at(key);
// call the handler
handler(data);
}
}
catch (const std::out_of_range&)
{
// todo decide what you want to do with incorrect messages here
}
}
//-----------------------------------------------------------------------------
// and handle a test message in main
int main()
{
const std::string data{ "key1,Hello" };
handle_message(data);
}