passing address to sprintf()

[randomprocess]

How do I do this guys....

char *buff2 = " "; // is malloc'd in real code.
sprintf(&buff2[2],"xx"); // is sprintf(&buff2[2],"%02X",*ptr) in real code.
printf("%s\n");

obviously trying to write "xx" to &buff2+2 and &buff2+3.

 

[Salem]

Well you should sprintf to a temporary buffer first, then use memcpy() to move two chars to your destination buffer.

sprintf would always append a \0 to whatever it did, so if buff2[4] was really important to you, it would be trashed.

But as far as general syntax goes, it's a valid thing to do.


--
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.

 

[randomprocess]

That was my impression (that it was valid). Problem is that it accesses the data rather than the address of the data. &buff2[2] and buff[2] are equivalent... and I did not think they should be... I very much did not think they should be... bug in the compiler?

Thanks for the post.

 

[Salem]

I think you would need to post some real code, because there are too many mistakes in the paraphrased code to be really sure.

I mean, when you start saying things like "&buff2+2 and &buff2+3", then you're way off base if your intent is to try and write characters to some position in a string that buff2 points to.

&buff2+2 is valid syntax, it's just that it means something completely different. You can't just go by "well it compiles".



--
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.