problem with vsprintf

[rajanandhini]

Hi,

When I try to compile the following code, I get an additional message from the buffer.

The code that we use has,
buf[0] = '\0';
va_start(va, fmt);
vsprintf(buf, fmt, va);
va_end(va);

len = fprintf(work,"%s",buf);

The buffer should only contain the content of fmt. But, it also contains the text "parent information" along with the content of fmt. i.e, if the value of fmt is "hi", the value of buf should also be "hi". But the actual value that we get is, "parent informationhi".

Please help.

Thanks,

nan

[Dennis Handly]

buf[0] = '\0';

You don't need this. The following seems fine:
va_start(va, fmt);
vsprintf(buf, fmt, va);
va_end(va);

>The buffer should only contain the content of fmt. But, it also contains the text "parent information" along with the content of fmt.

It shouldn't have this. What is in fmt?

len = fprintf(work,"%s",buf);

It is silly to use fprintf(%s), you should call fputs or fwrite. Or you could have called vfprintf to start with.

[rajanandhini]

fmt is a character pointer and it contains the string, "hi am fine"

[Dennis Handly · Accepted solution]

>fmt is a character pointer and it contains the string, "hi am fine"

What you are saying can't happen unless you have your own bogus version of vsprintf.

If you set a breakpoint on vsprintf, are you in libc when you hit it? What does "bt" give?

[Dennis Handly]

Or you can use "info func vsprintf" to see how many you have.

[Peter Nikitka]

Hi,

how is the variable buf declared?
Does 'buf' point to an allocated chunk of memory big enough to hold the varargs?
Best use vsnprintf() in that cases because not buffer overrun can occure when correctly used.

mfG Peter