Thread: sprintf()

Sounds like a homework question...

Hint:

Code:

char theString[256] = "This is the first part";
sprintf(theString, "%s, %s" theString, "this is the second part");

At the end of that, theString = "This is the first part, this is the second part". Now I'm sure you can figure out the rest

you need to use the return value of sprintf http://linux.die.net/man/3/sprintf

Code:

char buf[BUF_SIZ];
int len = 0;
int ret = sprintf(buf,"%d ", 1);

if(ret < 0)
{
   perror("sprintf");
   return ret;
}

len += ret;

ret = sprintf(buf+len, "%d ", 2);

etc

I hope you can figure out how to make it in the loop

> sprintf(theString, "%s, %s" theString, "this is the second part");
Bad idea.
Like most C functions, this one is NOT safe when you use overlapping source and destination strings (in this case, theString).

Sure, you may get lucky in this case, but try and put anything before the first %s, and you're in for a rude awakening.

Not to mention there's a missing comma.

But you can use something like this . . .

Code:

sprintf(theString + strlen(theString), ", %s", "this is the second part");

You could even record the length of the string, since strlen() is a bit expensive to compute.

Code:

int len = 0;
/* ... */
while(condition) {
    len += sprintf(theString + len, ", %s", "this is the second part");
}

Note that this is ignoring the possibility of buffer overruns, which probably isn't the best idea . . . .

snprintf() is C99, and the OP said "sprintf". I was just suggesting that you could at least check to make sure len never goes above, say, 10 characters less than the maximum. (Assuming you're not adding more than 10 characters with each sprintf() call.)

Oops my bad. One of those things I thought was right... thanks for pointing it out