Reduce cyclomatic complexity - c++

Question

I'm writing an NMEAParser library. As its name suggests, it parses NMEA sentences. Nothing crazy.
Its entry point is a function that accepts an NMEA string as its only parameter and looks at its beginning to pass it to the right decoder. Here is the function:
bool NMEAParser::dispatch(const char *str) {
if (!str[0]) {
return false;
}
//check NMEA string type
if (str[0] == '$') {
//PLSR245X
if (str[1] == 'P' && str[2] == 'L' && str[3] == 'S' && str[4] == 'R' && str[5] == ',' && str[6] == '2' && str[7] == '4' && str[8] == '5' && str[9] == ',') {
if (str[10] == '1')
return parsePLSR2451(str);
if (str[10] == '2')
return parsePLSR2452(str);
if (str[10] == '7')
return parsePLSR2457(str);
} else if (str[1] == 'G' && str[2] == 'P') {
//GPGGA
if (str[3] == 'G' && str[4] == 'G' && str[5] == 'A')
return parseGPGGA(str);
//GPGSA
else if (str[3] == 'G' && str[4] == 'S' && str[5] == 'A')
return parseGPGSA(str);
//GPGSV
else if (str[3] == 'G' && str[4] == 'S' && str[5] == 'V')
return parseGPGSV(str);
//GPRMC
else if (str[3] == 'R' && str[4] == 'M' && str[5] == 'C')
return parseGPRMC(str);
//GPVTG
else if (str[3] == 'V' && str[4] == 'T' && str[5] == 'G')
return parseGPVTG(str);
//GPTXT
else if (str[3] == 'T' && str[4] == 'X' && str[5] == 'T')
return parseGPTXT(str);
//GPGLL
else if (str[3] == 'G' && str[4] == 'L' && str[5] == 'L')
return parseGPGLL(str);
}
//HCHDG
else if (str[1] == 'H' && str[2] == 'C' && str[3] == 'H' && str[4] == 'D' && str[5] == 'G')
return parseHCHDG(str);
}
return false;
}
The problem I have is that this function's cyclomatic complexity is quite high, and my SonarQube complains about it:
It's not really a problem as the code is quite easy to read. But I was wondering how I could reduce its complexity while still keeping it simple to read and efficient.

Answer 1

You can simplify this quite a lot:
if (std::string_view{str, 10} == "$PLSR,245,")
{
switch (str[10])
{
case '1' : return parsePLSR2451(str);
case '2' : return parsePLSR2452(str);
case '7' : return parsePLSR2457(str);
}
}
else if (std::string_view{str + 1, 2} == "GP")
{
auto s = std::string_view{str + 3, 3};
if (s == "GGA")
return parseGPGGA(str);
if (s == "GSA")
return parseGPGSA(str);
// ... etc
}
else if (std::string_view{str + 1, 5} == "HCHDG")
{
return parseHCHDG(str);
}
return false;
There's no extra strings being constructed either, so it should be at least as efficient.