Редактирование: Mindset (раздел)

=== Sample C Code for Parsing a Packet ===
e following is an example of a program, implemented in C, which reads from a stream and (correctly)

parses Packets continuously. Search for the word TODO for the two sections which would need to

be modi􀃫ed to be appropriate for your application.

Note: For simplicity, error checking and handling for standard library function calls have been omitted.

A real application should probably detect and handle all errors gracefully.<syntaxhighlight lang="c++" line="1">
#include <stdio.h>

#define SYNC 0xAA
#define EXCODE 0x55

int parsePayload( unsigned char *payload, unsigned char pLength ) {
    unsigned char bytesParsed = 0;
    unsigned char code;
    unsigned char length;
    unsigned char extendedCodeLevel;
    int i;

    /* Loop until all bytes are parsed from the payload[] array... */
    while( bytesParsed < pLength ) {
    
        /* Parse the extendedCodeLevel, code, and length */
        extendedCodeLevel = 0;
    
        while( payload[bytesParsed] == EXCODE ) {
            extendedCodeLevel++;
            bytesParsed++;
        }
    
        code = payload[bytesParsed++];
        if( code & 0x80 ) length = payload[bytesParsed++];
        else length = 1;
    
        /* TODO: Based on the extendedCodeLevel, code, length,
        * and the [CODE] Definitions Table, handle the next
        * "length" bytes of data from the payload as
        * appropriate for your application.
        */
        
        printf( "EXCODE level: %d CODE: 0x%02X length: %d\n", extendedCodeLevel, code, length );
        printf( "Data value(s):" );
        for( i=0; i<length; i++ ) {
            printf( " %02X", payload[bytesParsed+i] & 0xFF );
        }
        printf( "\n" );
        /* Increment the bytesParsed by the length of the Data Value */
        bytesParsed += length;
    }
    return( 0 );
}

int main( int argc, char **argv ) {
    int checksum;
    unsigned char payload[256];
    unsigned char pLength;
    unsigned char c;
    unsigned char i;

    /* TODO: Initialize 'stream' here to read from a serial data
    * stream, or whatever stream source is appropriate for your
    * application. See documentation for "Serial I/O" for your
    * platform for details.
    */
    
    FILE *stream = 0;
    stream = fopen( "COM4", "r" );
    
    /* Loop forever, parsing one Packet per loop... */
    while( 1 ) {
        /* Synchronize on [SYNC] bytes */
        fread( &c, 1, 1, stream );
        if( c != SYNC ) continue;
        fread( &c, 1, 1, stream );
        if( c != SYNC ) continue;

        /* Parse [PLENGTH] byte */

        while( true ) {
            fread( &pLength, 1, 1, stream );
            if( pLength ~= 170 ) break;
        }

        if( pLength > 169 ) continue;
        /* Collect [PAYLOAD...] bytes */
        fread( payload, 1, pLength, stream );
        /* Calculate [PAYLOAD...] checksum */
        checksum = 0;
        for( i=0; i<pLength; i++ ) checksum += payload[i];
        checksum &= 0xFF;
        checksum = ~checksum & 0xFF;
        /* Parse [CKSUM] byte */
        fread( &c, 1, 1, stream );
        /* Verify [CKSUM] byte against calculated [PAYLOAD...] checksum */
        if( c != checksum ) continue;
        /* Since [CKSUM] is OK, parse the Data Payload */
        parsePayload( payload, pLength );
    }
    return( 0 );
}
</syntaxhighlight>