C variant of vector?

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06-12-2008
TriKri

C variant of vector?

Hi!

if you use scanf("%as", &s); memory will be allocated to store just as many characters plus one null character as the string contains. But how do scanf know how many characters the string contains? Or does scanf extend the allocated memory in the meantime?

Ok, here is the problem I want to solve: The user shall enter an arbitrary number of bytes (in integer or hexadecimal form) to the program, and they shall all end up in an array big enough to store them all. When the user has entered all the bytes he will press some special key, like f for finished. Is it possible to make them all end up in an array without first storing them in a linked list? Note that there's no way to tell how many or how few bytes will be entered.
06-12-2008
Salem

> if you use scanf("%as", &s); memory will be allocated to store just as many characters plus one null character as the string contains.
Well there's your first problem, no it doesn't.
What it will do is overwrite memory you don't own without warning. Perhaps you're interpreting the lack of a crash as success.

Whatever it is you're reading, you need to read it in fixed sized blocks and use a linked list, or use realloc to extend the space available.
06-12-2008
tabstop

Quote:

Originally Posted by TriKri

Hi!

if you use scanf("%as", &s); memory will be allocated to store just as many characters plus one null character as the string contains. But how do scanf know how many characters the string contains? Or does scanf extend the allocated memory in the meantime?

This is a GNU extension, and can lead you into trouble. %a reads in a floating-point number (according to the C99 standard, anyway), so if you decide to add in -ansi, or -std=c99, or something, it will stop working.

Quote:

Originally Posted by TriKri

Ok, here is the problem I want to solve: The user shall enter an arbitrary number of bytes (in integer or hexadecimal form) to the program, and they shall all end up in an array big enough to store them all. When the user has entered all the bytes he will press some special key, like f for finished. Is it possible to make them all end up in an array without first storing them in a linked list? Note that there's no way to tell how many or how few bytes will be entered.

You'll have to store them somewhere; if you feel like taking the performance penalty, you can write them to a temporary file while counting bytes, and then read back from that file. I suppose the question is really "what are you trying to do?" If its something you can achieve with buffered input, then go for that