Stupid C strings..... [fixed]

Sharp101

ok, this should be a quick question....


writing a Sender/Reciever program

Both files send string "ACK" to eachother, both defined in each file the same:
char ack[3]="ACK"; //defined ACK


sooo now....


before I send or recieve anything, I print out what the variable is
both have this line
printf("expected ack: %s \n",ack);

now lets see what the two files actually print.

Sender prints
expected ack: ACÿÏ1

Reciever prints
expected ack: ACKÿ


So when I send this to the other file, it doesn't compare properly.


Ideas?

(summary.... the same string declared the same way in two different files prints differently. Why?)

MiracleManS

Are you sure that you're not adding extra characters to the end by accident and/or there isn't a problem with this in one of the settings of the variable you're doing?

I know in PHP now there's an add-on to the timestamp string if you're not careful.

taeric

Is there a reason you aren't null terminating those? I thought a string in C was typically a null terminated character array.

so, shouldn't it be?

char ack[4] = "ACK\0";

Sharp101

Thanks Taeric, that got it....


now onto the segmentation faults!

taeric

Just a quick pointer, odds are that not null terminating the strings were causing the segmentation faults.

Sharp101

nope, opening a file that doesnt exist and trying to read from it does.

homeobocks

When I saw the subject for this thread, I thought He forgot to null-termitate the string. Lo and behold.

sirSolarius

taeric wrote:

Is there a reason you aren't null terminating those? I thought a string in C was typically a null terminated character array.

so, shouldn't it be?

char ack[4] = "ACK\0";

When you quote a string, it includes the null terminator. Now your string is:

ack[0]='A'
ack[1]='C'
ack[2]='K'
ack[3]='\0' (the one you put in)
ack[4]='\0' (the one that the string automatically puts in)

ack[4] is not ack's allocated memory, so you're shoving a 0 somewhere that a 0 might not want to be.

Also, you're pointing ack to "ACK" in your data/strings section, rather than copying the letters A, C, K and \0 into ack.

The correct version is:

char ack[4];
strcpy(ack, "ACK");

or

char *ack = "ACK";