checksum_NMEA( input_str, result );
Parameters
| Parameter | Type | Description |
|---|---|---|
input_str |
const unsigned char * |
The NUL terminated input string for which the NMEA checksum must be calculated |
result |
unsigned char * |
Storage buffer to the calculated NMEA checksum |
Return Value
| Type | Description |
|---|---|
unsigned char * |
Pointer to the storage buffer with the NMEA checksum result |
Description
The function checksum_NMEA() calculates the checksum in NMEA messages. The NMEA protocol is mainly used in marine equipment. The string may optionally be starting with a $ character. This character is automatically ignored by the checksum calculation algorithm. The end of the NMEA is reached when the algorithm detects the end of the NUL terminated string, a newline character or a * character.
The function returns the checksum as a NUL terminated string with two hexadecimal characters stored in a caller provided buffer. For this reason the calling function must provide a buffer which can at least contain 3 bytes. If NULL is provided as either the pointer to the input string or the pointer to the result buffer the function returns NULL. Otherwise the return value is a pointer to the beginning of the result string.