MSP430FR2355: strcat not working??

Steve Wenner

Part Number: MSP430FR2355

Can someone tell me what I am doing wrong in this small block:

        mssg = Send;
        strcpy(Send, "HelloWorld");
        m = strlen(mssg);
        CRC_Result = CRC(mssg, m);
        CRC_char[0] = (CRC_Result >> 8) & 0xFF;
        CRC_char[1] = (CRC_Result & 0xFF);
        mssg = (strcat(mssg, (const char*)CRC_char));

    char *mssg, junk, CRC_char[2];
    uint CRC_Result, m;
    char Send[BUFFER_SIZE] = {[0 ... BUFFER_SIZE-1] = 0xFF};

BUFFER_SIZE = 30.

The CRC_Result has been verified and is good. It is an unsigned int. However when I do the concatentation I get the CRC added to the message AND then after that I get the byte swapped CRC added to the message. I have tried all kinds of variants and can't seem to find what I am doing wrong? If I concat a string constant like "Today" to my mssg it works fine. CRC_char looks as expected after CRC_Result.

Thanks

over 5 years ago

0 Keith Barkley over 5 years ago

Guru 42205 points

strcat() needs a string with a nul char at the end:

CRC_char[2] = '\0';

You clobbered memory.

In general, *all* the str* functions require strings with '\0' at the end.

0 Steve Wenner over 5 years ago in reply to Keith Barkley

Genius 3240 points

So increasing CRC_char[ 3 ] should do the trick?

No need to memset with '\0'?

My ultimate goal is to add CRC and '\n' to my messages.

The following seems to work (at least for the one or two messages I tried).

        mssg = strcat(strcat(mssg, CRC_char), "\n");

Do you see anything wrong with this?

Thanks

0 David Schultz over 5 years ago in reply to Keith Barkley

Guru 25185 points

strncat() would do the job here as the "from" string doesn't need to be null terminated.

0 Keith Barkley over 5 years ago in reply to Steve Wenner

Guru 42205 points

yes, making it 3 characters should suffice.

no need to memset, just set the final char to '\0'

you can daisy chain strcat like that since it returns a pointer to the first arg, but it is a bit odd and most people will puzzle over it since you usually throw away the return value.

0 David Schultz over 5 years ago in reply to David Schultz

Guru 25185 points

But, if the first of those two bytes is a zero then it will not copy the second. And if you send that string to something expecting a null terminated string it would also fail if the second byte was zero.

0 Keith Barkley over 5 years ago in reply to David Schultz

Guru 42205 points

strncat() would have the same issue.

The strXXX functions do not handle binary data very well.

0 Keith Barkley over 5 years ago in reply to David Schultz

Guru 42205 points

NMEA GPS sentences handle this problem by formatting the checksum as ASCII characters using hex, so no '\0'.

0 Steve Wenner over 5 years ago in reply to Keith Barkley

Genius 3240 points

Maybe it wasn't said but if you look at my first post

CRC_char [2] is type char.

I took TI's CRC and modified it to take a pointer to a char type as input but it still fed out an integer which I fed into my character array. The '\0' was a byproduct of using the str functions (or so I believe).

I went ahead and moved to strncat as you suggested earlier and that seems to work fine

0 Keith Barkley over 5 years ago in reply to Steve Wenner

Guru 42205 points

The char type is simply an 8 bit integer. Generally you want to limit yourself to the "printable" ASCII characters to avoid surprises.

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MSP430FR2355: strcat not working??