Stack around the variable 'dim'(not an array) was corrupted

Question

I'm trying to read from a binary file, using fstream, some data I have previously written there.

The problem is that after getting to the end of the function the message in the subject is shown

The code is the following:

ifstream in("contrib.bin", ios::in | ios::binary );

char *nume, dim;
in.read((char*)&dim, sizeof(int));
nume = new char[dim + 1];
in.read(nume, dim);
nume[dim] = '\0';
double imp;
in.read((char*)&imp, sizeof(double));

delete [] nume;

Now, I've done my homework and looked for this issue, but the other people who faced it had arrays, whereas my variable is a simple char.

Can someone point me to the right direction, please?

Instead of raw arrays and new and delete, use a std::vector or a std::string, depending on how you intend to use the data. To pass a pointer to the first byte in a vector or a string v, use &v[0]. Note however that as opposed to the current code this is UB for size 0, so you need to check for size 0 (if that can occur). — Cheers and hth. - Alf
– Cheers and hth. - Alf, Commented Jan 11, 2013 at 16:53

simonc · Accepted Answer · 2013-01-11 17:06:32Z

13

The code

char dim;
in.read((char*)&dim, sizeof(int));

defines a 1 byte char then reads sizeof(int) bytes (which is likely to be greater that 1) into it. This is invalid and may corrupt your stack.

If you need to read sizeof(int) bytes, declare dim as int. Otherwise, change the number of bytes you read to 1. It'd be best if you also used sizeof(dim) to ensure that you only read as many bytes as you've provided storage for:

in.read((char*)&dim, sizeof(dim));

edited Jan 11, 2013 at 17:06

answered Jan 11, 2013 at 16:28

simonc

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7 Comments

netcoder Over a year ago

It could corrupt the stack. For all we know it could also send the computer flying across the room. ;-)

Agentlien Over a year ago

"reads 4 bytes" is not necessarily true, since the sizeof(int) depends on the platform in more ways than one (size of a byte and amount of bits used for an int).

simonc Over a year ago

@netcoder I know this isn't strictly true in general but since the question mentioned a stack corruption error I thought it was a fair assumption here. I've updated my answer along the lines you were suggesting though.

Agentlien Over a year ago

Much better. :) You get a tasty +1 to munch on.

Daniel Fischer Over a year ago

@simonc You can't assume eight-bit bytes. They may be larger. If CHAR_BIT >= 16, sizeof(int) could be 1.

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Luchian Grigore · Accepted Answer · 2013-01-11 16:28:12Z

7

in.read((char*)&dim, sizeof(int)); is not correct, dim only holds sizeof(char) which is one, but you're attempting to read sizeof(int) into it.

All gloves are off after this.

answered Jan 11, 2013 at 16:28

Luchian Grigore

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2 Comments

Pete Becker Over a year ago

Unless sizeof(int) happens to be 4. Unusual, but not impossible.

Luchian Grigore Over a year ago

@PeteBecker do you mean "happens to be 1"?

rerun · Accepted Answer · 2013-01-11 16:29:10Z

2

Well you define a character then read in the size of an int. That would be the first issue

char *nume, dim;
in.read((char*)&dim, sizeof(char));

answered Jan 11, 2013 at 16:29

rerun

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