The declarations:
allocate space on the stack for two pointers to characters. And the size of a is the size of a pointer (4 bytes in a 32-bit application; 8 bytes in a 64-bit application).
With these declarations, the initial value of these pointers is whatever random bytes happen to have been on the stack. When you copy data or read data into an area pointed to by an uninitialized pointer, you will get a memory fault, a bus error, or overwrite data at some random location depending on what random bytes on the stack happen to underly your pointers. If you malloc() space for arrays of characters and assign the pointers that malloc() returned to your pointers, then you won't be overwriting a random location in memory, but you would still have a problem because the sizeof(a) in:
is the size of the pointer; not the number of bytes allocated by malloc() to the array pointed to by a.
The declarations:
allocate two arrays of 100 bytes each on your stack. And the size of a is 100 bytes.
void main()
{
int a={1,2,3,4,5,6,7,8,9,10};
int *p=a;
int *q=&a;
cout<<q-p+1<<endl;
}
The output is 10, how?
if we give cout<<q it will print the address, value won't print....
if we give cout<<p it will print the address, value won't print....
p has the base addr; q... (1 Reply)
All ..
I am having a pointer array . And trying to store the addess into that pointer array . please see below the problem i faced
code:
int cnt1;
char *t_array;
char *f_array;
for(cnt1=0; cnt1<1000; cnt1++)
{
t_array =... (1 Reply)
If one wants to get a start address of a array or a string or a block of memory via a function, there are at least two methods to achieve it:
(1) one is to pass a pointer-to-pointer parameter, like:
int my_malloc(int size, char **pmem)
{
*pmem=(char *)malloc(size);
if(*pmem==NULL)... (11 Replies)
Hi all,
Can anyone provide help with getting the right syntax regarding array/pointers in C in the following code? Can't locate a specific example which clarifies this...
Say I declare a typedef to an array of pointers to some type...
/**
* An array of ptrs to sections
*/
typedef... (4 Replies)
if i create an array of pointers to a structure "struct node" as:
struct node *r;
and create "n" number of "linked lists" and assign it to the various struct pointers r using some function with a return type as structure pointer as:
r=multiplty(.......) /*some parameters*/
is... (2 Replies)
Hi guys,
Besides the points bellow, what would best practices for scripting be ?
1) set the PATH
2) unset the current environment (set -u ?)
3) (re)set the IFS to default value - space (IFS="" <- is this correct ?)
4) check the return code for each action inside the script (cd, rsync,... (1 Reply)
I am struggling with the pointer to 2D-array (cf: 2D array of pointers). Can anybody help me elaborate how the pointer x moves in the memory to access the individual of y, especially the high lighted lines?
I have talked to one of the curators of the forum, but I am still not quite clear.
Here... (1 Reply)
Discussion started by: yifangt
1 Replies
LEARN ABOUT SUNOS
bsdmalloc
bsdmalloc(3MALLOC)bsdmalloc(3MALLOC)NAME
bsdmalloc - memory allocator
SYNOPSIS
cc [ flag ... ] file ... -lbsdmalloc [ library ... ]
char *malloc(size);
unsigned size;
int free( ptr);
char *ptr;
char *realloc( ptr, size);
char *ptr;
unsigned size;
These routines provide a general-purpose memory allocation package. They maintain a table of free blocks for efficient allocation and coa-
lescing of free storage. When there is no suitable space already free, the allocation routines call sbrk(2) to get more memory from the
system. Each of the allocation routines returns a pointer to space suitably aligned for storage of any type of object. Each returns a
null pointer if the request cannot be completed.
The malloc() function returns a pointer to a block of at least size bytes, which is appropriately aligned.
The free() function releases a previously allocated block. Its argument is a pointer to a block previously allocated by malloc() or real-
loc(). The free() function does not set errno.
The realloc() function changes the size of the block pointed to by ptr to size bytes and returns a pointer to the (possibly moved) block.
The contents will be unchanged up to the lesser of the new and old sizes. If the new size of the block requires movement of the block, the
space for the previous instantiation of the block is freed. If the new size is larger, the contents of the newly allocated portion of the
block are unspecified. If ptr is NULL, realloc() behaves like malloc() for the specified size. If size is 0 and ptr is not a null pointer,
the space pointed to is freed.
The malloc() and realloc() functions return a null pointer if there is not enough available memory. They return a non-null pointer if size
is 0. These pointers should not be dereferenced. When realloc() returns NULL, the block pointed to by ptr is left intact. Always cast the
value returned by malloc() and realloc().
If malloc() or realloc() returns unsuccessfully, errno will be set to indicate the following:
ENOMEM size bytes of memory cannot be allocated because it exceeds the physical limits of the system.
EAGAIN There is not enough memory available at this point in time to allocate size bytes of memory; but the application could try
again later.
Using realloc() with a block freed before the most recent call to malloc() or realloc() results in an error.
Comparative features of the various allocation libraries can be found in the umem_alloc(3MALLOC) manual page.
brk(2), malloc(3C), malloc(3MALLOC), mapmalloc(3MALLOC), umem_alloc(3MALLOC)WARNINGS
Use of libbsdmalloc renders an application non-SCD compliant.
The libbsdmalloc routines are incompatible with the memory allocation routines in the standard C-library (libc): malloc(3C), alloca(3C),
calloc(3C), free(3C), memalign(3C), realloc(3C), and valloc(3C).
21 Mar 2005 bsdmalloc(3MALLOC)