cstring.h question

[keeler1]

Many of the functions is cstring take a char * and return one as well.

For example strtok takes some char * and returns some tokenization of it.

I am using this function and need to know a couple of things. Is the char * returned dynamically allocated or is it just a pointer into the inputted array of characters. And 2, if it is dynamically allocated will c take care of it since I didnt allocate the memory or do I have to delete it myself

[mike_g]

Its just points to a location within the string, it does not allocate separate space or anything.

[Lster]

I really wasn't sure of this myself, either. I had a look in LibC, though:


— Function: char * strtok (char *restrict newstring, const char *restrict delimiters)

A string can be split into tokens by making a series of calls to the function strtok.

...

But look at this:


Warning: Since strtok and wcstok alter the string they is parsing, you should always copy the string to a temporary buffer before parsing it with strtok/wcstok (see Copying and Concatenation). If you allow strtok or wcstok to modify a string that came from another part of your program, you are asking for trouble; that string might be used for other purposes after strtok or wcstok has modified it, and it would not have the expected value.

The string that you are operating on might even be a constant. Then when strtok or wcstok tries to modify it, your program will get a fatal signal for writing in read-only memory. See Program Error Signals. Even if the operation of strtok or wcstok would not require a modification of the string (e.g., if there is exactly one token) the string can (and in the GNU libc case will) be modified.

Here's the link:

http://www.gnu.org/software/libc/manual/html_node/Finding-Tokens-in-a-String.html#Finding-Tokens-in-a-String

Hope that helps,
Lster