getting access violation error while accessing allocated memory

Question

I have allocated memory of 100 MB using malloc

block = (char *)malloc(sizeof(10485760));  // char *block is a global variable

and then I assigned value in block to some local variable say localblock

char *localblock = block;

when I tried to access location after 1 MB and copying string in that location im getting access violation error

int si = 1048576;

for (int i=0; i < si; ++i)
    ++localptr;

strcpy(localblock,"random_string"); <--- im getting error here .please help me

Also remove the C++ tag, this is C code - and in C you don't need to cast the return of `malloc` either — UnholySheep, Jun 04 '17 at 12:36
_"I have allocated memory of 100 MB using malloc ..."_ no you have not — Richard Critten, Jun 04 '17 at 12:37
There's a better way to advance a pointer by X elements instead of a loop: `localptr += si;`. — Some programmer dude, Jun 04 '17 at 12:38
As @UnholySheep, C and C++ are very different languages. Only tag your question with one of them. — tambre, Jun 04 '17 at 12:40

score 3 · Accepted Answer · answered Jun 04 '17 at 12:39

3

block = (char *)malloc(sizeof(10485760));

is allocating only sizeof(int) number of bytes, when you access memory beyond that its will end up accessing invalid memory and program might crash

answered Jun 04 '17 at 12:39

Pras

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CIsForCookies · Answer 2 · 2017-06-04T12:41:35.613

-1

when you use malloc the allocation is not guaranteed.

block = (char *)malloc(sizeof(10485760));is trying to allocate space for 10485760 which is an int - meaning 4/8 bytes on 32/64-bit machine. "random_string" is longer then that, hence your error

edited Jun 04 '17 at 12:41

answered Jun 04 '17 at 12:37

CIsForCookies

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`sizeof(10485760)` is the size needed for the litteral `10485760` – Ilario Pierbattista Jun 04 '17 at 12:39

getting access violation error while accessing allocated memory

2 Answers2