'byte' : ambiguous symbol error when using of Crypto++ and Windows SDK

Question

In Visual Studio 2012, I'm trying to encrypt a file with Crypto++ library with AES encryption and CBC mode as following :

#include <Windows.h>
#include "aes.h"
#include "modes.h"
#include "files.h"
#include <Shlwapi.h>

using namespace CryptoPP;

INT main(INT argc, CHAR *argv[])
{
    CHAR szKey[16] = {0};
    CHAR szInitVector[AES::DEFAULT_KEYLENGTH] = {0};

    StrCpyA(szKey, "qqwweeff88lliioo");
    StrCpyA(szInitVector, "eerrttooppkkllhh");

    CBC_Mode<AES>::Encryption encryptor((byte*)szKey, AES::DEFAULT_KEYLENGTH, (byte*)szInitVector);
    FileSource fs("in.txt", true, new StreamTransformationFilter(encryptor, new FileSink("out.aes")));

    return 0;
}

In Qt it does work!, But here I wondered why got the following error :

error C2872: 'byte' : ambiguous symbol
could be 'c:\program files (x86)\windows kits\8.0\include\shared\rpcndr.h(164) : unsigned char byte'
or 'z:\cryptography\app_aesencryption\aes headers\config.h(237) : CryptoPP::byte'

Due to prevent of ambiguous symbol error, even I cast bellow statement with CryptoPP::byte* :

CBC_Mode<AES>::Encryption encryptor((CryptoPP::byte*)szKey, AES::DEFAULT_KEYLENGTH, (CryptoPP::byte*)szInitVector);

I didn't get any error for 'byte' : ambiguous symbol, But It give me many errors as :

error LNK 2038

By the way, I linked .lib file of Crypto++, So I think this error is Unlikely for this. Is last error related to CryptoPP::byte*? Is there any solution?

Remove `using namespace CryptoPP;` as this statement brings `CryptoPP::byte` into the global namespace and `rpcndr.h` has already typedef'd `unsigned char` as `byte` — Richard Critten, Aug 12 '18 at 11:39
@RichardCritten I tried with `CryptoPP::CBC_Mode` namespace directly. but it does not work. — BattleTested_закалённый в бою, Aug 12 '18 at 11:41
_"...does not work..."_ is not a problem report I can help you with. — Richard Critten, Aug 12 '18 at 11:42
The error message is pretty clear. Cast it to CryptoPP::byte*. — zdf, Aug 12 '18 at 11:43
@ZDF it give me a lot of `error LNK 2038` list when i try this --> `CryptoPP::byte*` — BattleTested_закалённый в бою, Aug 12 '18 at 11:46
So, it fixes the error. Go to linker options and add the CryptoPP library. — zdf, Aug 12 '18 at 11:48
@MohammadrezaPanahi **Rebuild all**. Rebuld also any used *.lib or *.obj from `z:\cryptography\`. — Daniel Sęk, Aug 12 '18 at 11:52
[`using namespace whatever` is a bad practice?](https://stackoverflow.com/q/1452721/995714). The larger the namespace the more chance you'll get problem — phuclv, Aug 12 '18 at 11:53
Check that the library you're trying to link is added to your options. — zdf, Aug 12 '18 at 11:58
[https://learn.microsoft.com/en-us/cpp/error-messages/tool-errors/linker-tools-error-lnk2038](https://learn.microsoft.com/en-us/cpp/error-messages/tool-errors/linker-tools-error-lnk2038) — Daniel Sęk, Aug 12 '18 at 12:10
Linker dependencies. Go to Project Properties | Linker | Input (if I correctly remember the commands). See [this](https://stackoverflow.com/a/51671578/1983409). — zdf, Aug 12 '18 at 12:12
You have incopatible settings for main app and cryptolib. For example different **Project->Properties->General->Platform Toolset**. Please show full error message. — Daniel Sęk, Aug 12 '18 at 12:36
If you don't like to write `CryptoPP::`, you can replace `using namespace CryptoPP` with `namespace crp = CryptoPP;` for instance. You can now use `crp::` in place of `CryptoPP::`, e. g. `crp::byte`. No ambiguities anymore but still less typing. — zett42, Aug 12 '18 at 15:40
Possible duplicate of [byte and ambiguous symbol due to using declarations?](https://stackoverflow.com/q/45125957/608639) Also see [Windows and "error C2872: 'byte' : ambiguous symbol"](http://crypto-users.996303.n3.nabble.com/Windows-and-quot-error-C2872-byte-ambiguous-symbol-quot-td7549.html) on the Crypto++ mailing list. — jww, Aug 13 '18 at 06:45
If you dont want to change the casts, you could do `using byte = CryptoPP::byte;` — M.M, Aug 13 '18 at 07:02

jww · Answer 1 · 2018-08-13T06:41:41.780

2

'byte' : ambiguous symbol error when using of Crypto++

We had to move byte from global namespace to CryptoPP namespace due to C++17 and std::byte. The change occurred at Commit 00f9818b5d8e, which was part of the Crypto++ 6.0 release.

Crypto++ used to put byte in the global namespace for compatibility with Microsoft SDKs. Without the global byte then you would encounter 'byte' : ambiguous symbol error again.

The error you are seeing is because you used using namespace CryptoPP; and the Microsoft kits still put a byte in the global namespace. The error did not surface under Qt because Qt does not put a byte in the global namespace.

There are several work-arounds discussed at std::byte on the Crypto++ wiki.

Incidentally, Microsoft kit code will break when it encounters a C++17 compiler and std::byte because of Microsoft's global byte. You will encounter the same error when using the Windows kits. Ironically, Microsoft employees authored C++ std::byte. Also see PR0298R0, A byte type definition.

edited Aug 13 '18 at 06:41

answered Aug 13 '18 at 06:36

jww

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"Microsoft kits still put a byte in the global namespace" ... the way it's done in platform headers makes it very unlikely that they even can stop doing that. Doesn't look like it's going to change. Instead of using byte cryptopp should just use uint8_t – Pavel P Aug 13 '18 at 06:49
1

@Pavel - Crypto++ is no longer part of the problem since its byte is now scoped. The problem is solely Microsoft and their headers now. Hindsight being 20/20 Crypto++ should have not attempted to be compatible with Microsoft SDK headers. But the decision was made in 1995 and it was hard to change until the C++17 breaks came. – jww Aug 13 '18 at 06:52
ms headers don't care about c++ (why should they?) they, they are C after all. They have that byte type in many structures, and it's reasonable to typedef it as an unsigned char. I wouldn't say that "the problem is solely Microsoft and their headers". They might as well say the problem is in c++ or whatever. Note, I don't deal with crypto and never had that byte problem myself, just tried to look how they define it in headers and if there was a way to prevent that typedef. – Pavel P Aug 13 '18 at 06:56
1

@Pavel - Microsoft blaming C++ or C++ blaming Microsoft works for me. I don't have a dog in that fight. I'm fine with it as long as the problem is not with Crypto++. – jww Aug 13 '18 at 06:57
It's not in cryptopp also. However, since there was std::byte added, it makes sense to use std::byte, or to change internal code to use uint8_t if it doesn't match semantics of std::byte (to avoid future confusion). Also, just curious, if cryptopp also typedefed it as unsigned char, then there wouldn't be any problem IMO – Pavel P Aug 13 '18 at 07:00
1

@Pavel - `uint8_t` typedef is not a good choice for Crypto++. We support too many compilers and platforms. Some of the time we will be able to use `` and `uint8_t`; and other times `` will be missing and we will have to provide a `typedef`. Part of the appeal of `byte`, `word16`, `word32` and friends was avoiding that problem (until C++17 and the byte problem arrived). And I cringe when thinking about the problems of removing the symbol after 28 years. Users will want to tar and feather us. – jww Aug 13 '18 at 07:16

BattleTested_закалённый в бою · Accepted Answer · 2018-08-13T18:05:54.453

0

The first problem solved with changing byte* to CryptoPP::byte* :

CBC_Mode<AES>::Encryption encryptor((CryptoPP::byte*)szKey, AES::DEFAULT_KEYLENGTH, (CryptoPP::byte*)szInitVector);

But to solving the second problem (error LNK 2038) :

This is related to link error, Every body that using of crypto++ in Visual Studio may have this problem.

First I was download library from bellow link for visual studio in which containt .sln (VS Solution) :

https://www.cryptopp.com/#download
I build the library via Batch Build as cryptlib project in both state (Debug|Win32 and Release|Win32)
Because I used of Debug mode, I linked cryptlib.lib in cryptopp700\Win32\Output\Debug in dependencies section.
Also add dependencies for header files...

But I forgot something in project properties :

Finally, I set Runtime Library option to Multi-threaded Debug (/MTd)

This option is in :

Project Properties
Configuration Properties
C/C++
Code Generation
Runtime Library

edited Aug 13 '18 at 18:05

answered Aug 12 '18 at 13:01

BattleTested_закалённый в бою

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Yes CRT configuration has to be compatible between all object modules. Repeat this also for Release configuration. – Daniel Sęk Aug 12 '18 at 14:00
@SHR yes my problem was also CRT configuration – BattleTested_закалённый в бою Aug 12 '18 at 17:25
2

*"Finally, I set Runtime Library option to Multi-threaded Debug (/MTd)..."* - Also see [Visual Studio | Runtime Linking](https://www.cryptopp.com/wiki/Visual_studio#Runtime_Linking) on the Crypto++ wiki. – jww Aug 13 '18 at 06:45

score 0 · Answer 3 · answered Aug 28 '21 at 05:30

I know this answer is not directly relating to Crypto++ & Windows SDK, but I know I found this while trying to figure out the same error when using the Nodejs addon library called Nan instead. I'm putting this answer here because it's in an accessible place for others who might run into similar issues to me.

I hadn't had too many issues compiling the project for a while but then ran into the same error as mentioned above. I wasn't using a byte symbol anywhere. There were dozens of errors pointing to libraries in the Windows SDK which also was conflicting with the cstddef header as the error addresses.

What I was able to do to fix the problem was rearranging the headers so that the Nan-related content (and any of my own header files that references it) was on top, above even the other standard C/C++ libraries. After that was done, the errors went away.

score 0 · Answer 4 · answered Mar 24 '22 at 13:42

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The decision is simpliest. Delete from your code 'using namespace std' and use namespace std:: before every operation instead.

answered Mar 24 '22 at 13:42

Dmitry Tuchin

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'byte' : ambiguous symbol error when using of Crypto++ and Windows SDK

4 Answers4