I was initializing array (unsigned short int) of size 100000000 in C 4.3.2 , and other two int array of size 1000000. But while submiting on Online judge, it was giving SIGSEGV error .
Therefor i decided to initialize my array dynamically with a default value 0, as adding value by loop takes much time.
My question is how to initialise array dynamically with a default value ?
You can use void *calloc(size_t nmemb, size_t size); function to initialize memory with 0,
The
calloc()function allocates memory for an array ofnmembelements of size bytes each and returns a pointer to the allocated memory. The memory is set tozero. Ifnmembor size is0, thencalloc()returns eitherNULL, or a unique pointer value that can later be successfully passed tofree().
calloc(number of elements, sizeof(type));
or you can also use memset() explicitly to initialize memory allocated by malloc() call.
Note: calloc() isn't magic either - it will also use a loop somewhere to replace the garbage with all zeroes.
You can't eliminate the initialization time, no matter what you do. The best you can do is to attempt to optimize it. 2 techniques come to mind:
Unrolling will probably be applied anyway by optimizing compiler.
You can also try to move the initialization overhead to a non-critical section. E.g., you can use static variables that will be zero-initialized upon program start. Or, in contrast, you can delay the initialization till first use (lazy initialization).
mmap()for UNIX-like systems orVirtualAlloc()on Windows; conveniently, these functions already zero the memory for you...