The C standard requires that NULL be defined in locale.h, stddef.h, stdio.h, stdlib.h, string.h, time.h, and wchar.h.
The C++ standard requires that NULL be defined in the c* header corresponding to each of those.
The C standard is very strict about the names a standard can define--each standard header must define precisely the names the standard requires that header to define. The only other names it can define are those that are reserved for the implementation, such as those starting with an underscore followed by another underscore or a capital letter.
The C++ standard is much more permissive in this respect--including any one standard header can have the same effect as including any or all other standard headers.
From a practical viewpoint, C++ implementations used to take quite a bit of advantage of this permissiveness--that is, including one standard header frequently defined the names from a number of other standard headers. More recent implementations tend to work more like the C standard requires, staying much closer to each header defining only the names required by to be defined by that header. They're still probably not as strict about it as the C standard requires, but much closer than they used to be (as a rule).
Answer from Jerry Coffin on Stack OverflowThe C standard requires that NULL be defined in locale.h, stddef.h, stdio.h, stdlib.h, string.h, time.h, and wchar.h.
The C++ standard requires that NULL be defined in the c* header corresponding to each of those.
The C standard is very strict about the names a standard can define--each standard header must define precisely the names the standard requires that header to define. The only other names it can define are those that are reserved for the implementation, such as those starting with an underscore followed by another underscore or a capital letter.
The C++ standard is much more permissive in this respect--including any one standard header can have the same effect as including any or all other standard headers.
From a practical viewpoint, C++ implementations used to take quite a bit of advantage of this permissiveness--that is, including one standard header frequently defined the names from a number of other standard headers. More recent implementations tend to work more like the C standard requires, staying much closer to each header defining only the names required by to be defined by that header. They're still probably not as strict about it as the C standard requires, but much closer than they used to be (as a rule).
C++03 section 18.1.2 says that NULL is defined in cstddef.
On some implementations, iostream may include cstddef, so including iostream would also give you NULL.
Hey, so when I was reading my gf's script for C classes, the tutor has written that
In some compilers there is no NULL but it can be easily replaced by a short macro
#define NULL 0
Does any compiler exist, which actually does not recognize NULL?
I'm writing a simple header that handles malloc returning a NULL pointer, is that good practice?
Old compilers and NULL
Hello. I'm a beginner and I'm doing the Advent of Code 2021 to develop my skills. I'm trying to use more malloc and realloc, because I think that's important. I just found out that these functions might return a NULL pointer in case they can't allocate memory, and that you're supposed to check whether the allocation worked or not.
I think having to do that in every instance I use any allocation function would be cumbersome, so I tried writing a header to use in all my Advent of Code programs that handles all of that for me. It tries to allocate memory CHANCES times, and if it fails, it exits the program. However, I wanted to ask whether that's a good practice to have for my future programs. Here's the header:
#include <stdio.h>
#include <stdlib.h>
#define CHANCES 5
static void allocError(void)
{
printf("allocation error: couldn't allocate more memory\n");
exit(1);
}
static void *altAlloc(void *pointer, size_t size)
{
void *temp;
int failchance = 0;
while (failchance++ < CHANCES) {
temp = realloc(pointer, size);
if (!temp)
continue;
pointer = temp;
return pointer;
}
allocError();
}It seems to be working perfectly when it's able to allocate the memory, but I don't know if it'd properly exit the program in case it's not. I think it is, though, since the code isn't that complicated.