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sprintf question.

Started by OrcishCoder Aug 4, 2005 at 11:11 AM 5 replies 750+ views

Original Post

Aug 4, 2005 at 11:11 AM

sorry my question might be stupid to you, but i really want to know a confident answer: char buffer[256]; . . . //buffer now contain string "Empty" let say. sprintf(buffer, "[ %s ]", buffer); <-- will this cause problem? I hope in final, buffer = "[ Empty ]". I cant show my code, because it is too long. And my program always got unpredictable bugs that very hard to reproduce. I checked my code, I suspect this sprintf might cause problem, but i dont sure, please help. Thanks in advance. regards, Martin

Deception666

Aug 4, 2005 at 11:15 AM

If copying occurs between strings that overlap, the behavior is undefined.

dyerseve

Aug 4, 2005 at 1:29 PM

Im no expert on sprintf (I stick to std::string and stringstreams and such), but that's probably not going to work. I tried it in Visual C++ 6.0, and on the implementation they use it does work. You get something like "[ [ [ [ ]". I'm not sure what the official ANSI specifications say about this, but I would just create a temporary buffer. (Actually I'd just use std::string.)

guyaton

Aug 4, 2005 at 2:47 PM

you could try:

char tempBuffer[256] = {0};sprintf( tempBuffer, "[ %s ]", buffer );memcpy( buffer, tempBuffer, sizeof(char)*256 );

SW INC

Aug 4, 2005 at 9:12 PM

why use the extra memcpy?

char tempbuffer[256];
.
.
.
//buffer now contain string "Empty" let say.

char buffer[256];

sprintf(buffer, "[ %s ]", tempbuffer);

works with out the extra waste of time for a memcpy (and is cleaner)

OrcishCoder

Author

OrcishCoder

Aug 4, 2005 at 9:47 PM

Thanks you guys. So I wont use that kind of method to copy string in future.

regards,
Martin

Aiursrage2k

Aug 5, 2005 at 9:26 AM

I dont think there would be a problem with that. Could use something like

char tmp[256];
int i;
tmp = '[';
for(i=1; i<254 && *(buffer+i); i++)
{
*(tmp+i) = *(buffer+i-1);
}
*(tmp+i) = ']';
*(tmp+i+1) = '\0';
for(i=0; *(tmp+i); i++)
{
*(buffer+i) = *(tmp+i);
}

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