* Here we open a channel and print all the messages we receive.
* SendMessage.c
#include <stdio.h>
#include <conio.h>
// To use CANlib, we need to include canlib.h and also link to canlib32.lib
// when compiling.
#include "canlib.h"
// The check method takes a canStatus (which is an enumerable) and the method
// name as a string argument. If the status is an error code, it will print it.
// Most Canlib method return a status, and checking it with a method like this
// is a useful practice to avoid code duplication.
void Check(const char* id, canStatus stat){
if (stat != canOK) {
char buf[50];
buf[0] = '\0';
canGetErrorText(stat, buf, sizeof(buf));
printf("%s: failed, stat=%d (%s)\n", id, (int)stat, buf);
void dumpMessageLoop(canHandle hnd, int channel_number){
// First declare some variables for holding the incoming messages. The
// incoming messages consist of the same parameters as an outgoing message,
// i.e. identifier (id), body (msg), length (dlc), and flags), as well as a
// timestamp.
canStatus stat = canOK;
long id;
unsigned int dlc, flags;
unsigned char msg[8];
DWORD timestamp;
printf("Listening for messages on channel %d, press any key to close\n", channel_number);
// Start a loop that loops until a key is pressed.
while (!_kbhit()){
// Call the canReadWait method to wait for a message on the channel. This
// method has a timeout parameter which in this case is set to 100 ms. If a
// message is received during this time, it will return the status code
// canOK and the message will be written to the output parameters. If no
// message is received, it will return canERR_NOMSG.
stat = canReadWait(hnd, &id, msg, &dlc, &flags, &timestamp, 100);
// Check that the returned status is OK (which means that a message has been received)
if (stat == canOK){
// If the message contains an error flag (which implies a different kind
// of error than if an error signal had been returned), an error message
// will be shown.
if (flags & canMSG_ERROR_FRAME){
printf("***ERROR FRAME RECEIVED***");
// If no error flag was found, the program prints the message.
else {
printf("Id: %ld, Msg: %u %u %u %u %u %u %u %u length: %u Flags: %lu\n",
id, dlc, msg[0], msg[1], msg[2], msg[3], msg[4],
msg[5], msg[6], msg[7], timestamp);
// Break the loop if something goes wrong, i.e. if we get a status code
// that is not canOK (taken care of above) and not canERR_NOMSG
else if (stat != canERR_NOMSG){
Check("canRead", stat);
void main(int argc, int* argv[]){
// Holds a handle to the CAN channel
canHandle hnd;
// Status returned by the Canlib calls
canStatus stat;
// The CANlib channel number we would like to use
int channel_number = 0;
// The first thing we need to do is to initialize the Canlib library. This
// always needs to be done before doing anything with the library.
printf("Opening channel %d\n", channel_number);
// Next, we open up the channel and receive a handle to it. Depending on what
// devices you have connected to your computer, you might want to change the
// channel number. The canOPEN_ACCEPT_VIRTUAL flag means that it is ok to
// open the selected channel, even if it is on a virtual device.
hnd = canOpenChannel(channel_number, canOPEN_ACCEPT_VIRTUAL);
// If the call to canOpenChannel is successful, it will return an integer
// which is greater than or equal to zero. However, is something goes wrong,
// it will return an error status which is a negative number.
if(hnd < 0){
// To check for errors and print any possible error message, we can use the
// Check method.
Check("canOpenChannel", (canStatus)hnd);
// and then exit the program.
printf("Setting bitrate and going bus on\n");
// Once we have successfully opened a channel, we need to set its bitrate. We
// do this using canSetBusParams. CANlib provides a set of predefined bus parameter
// settings in the form of canBITRATE_XXX constants. For other desired bus speeds
// bus paramters have to be set manually.
// See CANlib documentation for more information on parameter settings.
stat = canSetBusParams(hnd, canBITRATE_250K, 0, 0, 0, 0, 0);
Check("canSetBusParams", stat);
// Next, take the channel on bus using the canBusOn method. This needs to be
// done before we can read any messages from the bus.
stat = canBusOn(hnd);
Check("canBusOn", stat);
// Listening for messages
dumpMessageLoop(hnd, channel_number);
printf("Going of bus and closing channel");
// Once we are done using the channel, we go off bus using the
// canBusOff method. It take the handle as the only argument.
stat = canBusOff(hnd);
Check("canBusOff", stat);
// We also close the channel using the canCloseChannel method, which take the
// handle as the only argument.
stat = canClose(hnd);
Check("canClose", stat);
- Start this program, then run the SendMessage.c program from another
tutorial. Make sure to modify one of the programs so they use different
channel numbers which both should be connected.
- Send an error message to your program using the canMSG_ERROR_FRAME flag.
- The canReadSync method waits until there is a message on the channel, but
doesn't read the message. The canRead method reads messages, but returns
canERR_NOMSG immediately if there is no message on the channel. Rewrite the
program to use these methods instead of canReadWait.