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#How can I remove the first element of a dynamic array?
heavy girderBOT
silent bane
The only real good way to remove the first element is to move all the other elements back one
Unless you put in a large amount of effort into making a double ended queue data structure
boreal lintel
#include <stdio.h>
#include <memory.h>
#include <malloc.h>
// works for interger arrays, not general.
// to make it work with all arrays
// we need to use void *arr and also be
// informed for the size of each element.
//
// @return The array without the first element,
// returned element must be freed using free.
int *remove_first_element(int *arr, size_t size)
{
int *result = (int *) malloc(sizeof(int) *
(size - 1));
memcpy(result, arr + 1, sizeof(int) * (size - 1));
return result;
}
int main()
{
int arr[5] = {1,2,3,4,5};
int *res = remove_first_element(arr, 5);
for (int i = 0; i < 4; i++) {
printf("%d\n", res[i]);
}
}
you can do something lilke that
silent bane
fair point, I was only considering the scenario of an inplace removal
boreal lintel
xmm if you run the above snap of code, this is what it does
i think that it will work in your case
memcpy(result, arr + 1, sizeof(int) * (size - 1));
in this line, i just copy all the elements of the array after the first in a new array
isn't this what you want? 🧐 😂
( Sorry for my English, I might have some grammar mistakes )
heavy girderBOT
@raven cargo Has your question been resolved? If so, run !solved :)
wooden hemlock
@raven cargo If you want to get fancy, a single call to memmove() can move all your PIDs back one index in the array.
boreal lintel
xmm I had forgot about this function
wooden hemlock
If multiple threads are accessing the PID array at the same time, you'll want to protect all reads/writes to the PID array with some kind of synchronization.
To be clear, memcpy() will NOT work. It has to be memmove()
memcpy() only works when the source and destination don't overlap at all. memmove() works when the source and destination overlap.
What type is unavailablePIDs?
You might want to debug by doing something like this:
printf("unavailablePIDs = %p, PID+1 = %p\n", unavailablePIDS, PID+1);
Just to see if the pointers are coming out as expected.
boreal lintel
`memcpy()` only works when the source and destination don't overlap at all. `me...
@wooden hemlock you are right, i don't really think the case of overlapping here, fair point 😂
boreal lintel
```C
#include <stdio.h>
#include <memory.h>
#include <malloc.h>
// works for in...
Maybe you can use the code snap i wrote before, I mention it, but instead of returning the pointer you can just do
free(PID);
PID = result;
at the end of the function.
There is no memory overlap there, because I use a temporary variable.
dunno 😂
not a fancy solution
boreal lintel
I'm a little bit confused, what's the purpose of unavailablePIDs? xmm maybe I don't understand something.
wooden hemlock
What are you trying to do? Move all the elements to the left one position?
That is, pid[1] is moved into pid[0], pid[2] is moved into pid[1], etc.?
Hmmm, would that be:
memmove(unavailablePIDs, unavailablePIDs + 1, <size of pid array minus 1>);
Perhaps:
memmove(unavailablePIDs, unavailablePIDs + 1, sizeof(unavailablePIDs) - sizeof(unavailablePIDs[0]));
Assuming that unavailablePIDs is an array (i.e., not allocated using e.g. malloc)
(Edited the most recent message)
heavy girderBOT
heavy girderBOT