0xC0000005: Access violation writing location

Question

I have this function for reading text from files:

uintmax_t ResourcePack::getText(const string& file, char** data)
{
    *data = new char[static_cast<size_t>(size) + 1];
    fseek(_fileDescriptor, static_cast<long>(begin), SEEK_SET);
    fread(*data, static_cast<size_t>(size), 1, _fileDescriptor);
    *data[size] = '\0';
}

FILE* _fileDescriptor, uintmax_t size and uintmax_t begin are get in other code, not important here, but with correct values.

fseek and fread lines work fine. Actually, I have the file content in *data, but when the last line is executed, I got the access violation.

Why I can write into *data using fread, but not using *data[size] = '\0'?

Operator precedence - you want `(*data)[size]`, not `*data[size]`. — Paul R, Dec 17 '12 at 22:05
As @PaulR said... Generally I prefer to store a temporary `char*` variable and work with that in a function, then store it via the `char**` prior to returning. That way I avoid the extra syntax guff that can lead to errors and/or sore eyes. =) — paddy, Dec 17 '12 at 22:09
0xCC means you've read [uninitialized memory](https://stackoverflow.com/q/370195/995714) — phuclv, Oct 17 '17 at 04:34

score 5 · Accepted Answer · answered Dec 17 '12 at 22:07

5

You are having problems with operator precedence - you want (*data)[size], not *data[size].

answered Dec 17 '12 at 22:07

Paul R

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arg nice! I forgot that! Thanks! – danikaze Dec 17 '12 at 22:10

Mark B · Answer 2 · 2012-12-17T22:16:58.070

3

Your problem is the precedence of operators * and []. *data[size] means to access the nth char* in data, and then dereference its first character, not to get the nth character of the array pointed to by data.

You want (*data)[size] instead to perform the operations in the correct order.

EDIT: Since this is C++ you'd be better off using char*& to eliminate these sorts of problems, or much better off using vector and letting the standard library manage your memory for you!

edited Dec 17 '12 at 22:16

answered Dec 17 '12 at 22:08

Mark B

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I usually use std containers, but for this situation, a raw pointer is better in my case ;) I just forgot operators precedence :P – danikaze Dec 17 '12 at 22:45

0xC0000005: Access violation writing location

2 Answers2