Thread: using malloc dynamically...?

So, I'm trying to learn C as I'm going to be needing it quite extensively.

Now suppose I have a file containing an arbitrary list of characters

a z y a g y s h e p o................ etc

How do I read this in character by character, and store these in an array without knowing the size?

so basically, everytime i encounter a character, I have to allocate more memory and store it in my char*

I don't want to have a pre-sized buffer of, say, 100....

I know this might not be the best way to do it, but the point is, I need to learn how to create memory like this, on the fly, and attach this memory to my variable (which already has memory that was created dynamically)


Any help would be appreciated!

Originally Posted by NeonBlack

Basically:
Start with some amount of memory and start adding elements.
When you run out of room, increase the size and continue.

Thank you for your response.

How would I increase the memory?

Say I just have an int * a_ptr ?

I guess, I'm just having trouble with syntax and understanding the concept of how to add memory to a_ptr, and to assign values to that new memory location...

I mean, I know malloc calloc, but I don't know how I would assign that new memory to a_ptr while maintaining the memory currently at a_ptr

Originally Posted by quzah

Something like realloc.

Code:

if( ( newptr = realloc( oldptr, newsize ) ) != NULL )
{
    ...allocation worked...
    oldptr = newptr;
}
else
{
    ...allocation failed, you still have oldptr...
}

Quzah.

realloc!! I had no idea realloc existed. Just tried this, and it works.

excellent!

MK27, Comrade, you may want to check Snopes on that quote of yours.

If you are going to read characters from a file, you would be better served by using a function like stat() (UNIX) for example, to get the file size then allocate the appropriate amount of memory for the file in one go.

Another approach is to read a line at the time and discard it when it's time to read the next, if your application allows for it of course.

Originally Posted by Subsonics

If you are going to read characters from a file, you would be better served by using a function like stat() (UNIX) for example, to get the file size then allocate the appropriate amount of memory for the file in one go.

Another approach is to read a line at the time and discard it when it's time to read the next, if your application allows for it of course.

Right, I agree with you, however, I just need practice using malloc/calloc/realloc.