MSVC Compiler Error C4315 - No Documentation Found

Question

When compiling my app today, I encountered this warning (the code, I think, is irrelevant):

warning C4315: 'MyClass' : 'this' pointer for member 'MyClass::my_data_' may not be aligned 8 as expected by the constructor

I am not able to find any documentation about this warning, in either the online help, my locally-installed help, or via a google search. I did find one link on a MS forum:

No documentation for compiler warning C4315

But no information about the error itself.

Do you have any information about this error? I'm trying to fogure out how to fix it.

I have the "treat all warnings as errors" option set. Nonetheless, I'll edit my post. — John Dibling, Nov 19 '10 at 18:14
Are you building with /Wp64? This looks like a possible Win64 portability warning. C4312/C4313 (close at hand) are /Wp64 only. — Steve Townsend, Nov 19 '10 at 18:19
@Steve: No, I'm compiling in x64 and not detecting 64-bit compatibility issues. — John Dibling, Nov 19 '10 at 18:30
I can't find anything abot the error but not surprised that it's x64-related given the ref to 'aligned 8'. Any reason you can think of for the relevant `this` pointer to be screwy? Do you have custom packing on the class(es) involved? — Steve Townsend, Nov 19 '10 at 19:13
there is custom packing on some classes, but not this one. some of our classes are packet to 1-byte. — John Dibling, Nov 19 '10 at 19:19
@Hans: its going to be niegh impossible for me to post the code. but i can try — John Dibling, Nov 19 '10 at 19:19

score 7 · Accepted Answer · answered Nov 19 '10 at 19:20

7

I'd look for something (buried in a header?) changing the structure packing from the default.

The warning seems to be saying that whatever type MyClass::my_data_ is expects to be 8-byte aligned, but it's not being placed at that alignment inside MyClass.

Search for #pragma pack(some-number) directives that aren't reset with a #pragma pack().

Using #pragma pack(show) would probably be helpful, too.

answered Nov 19 '10 at 19:20

Michael Burr

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yep thatsd what i'm looking for – John Dibling Nov 19 '10 at 19:21

MSVC Compiler Error C4315 - No Documentation Found

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