CODEWITHSUNDEEP
c++mysql
zJay
zJay

Reputation: 3079

MYSQL headers conflict with STL <algorithm> in C++

// File test.cpp
#include <my_global.h>
#include <algorithm>
int main()
{
    return 0;
}

Compiled with: g++ -c -I /usr/local/mysql/include/mysql/ test.cpp, where /usr/local/mysql is the mysql install directory.Then the compiler report the following errors:

In file included from /usr/include/c++/4.4/algorithm:61, from test.cpp:3: /usr/include/c++/4.4/bits/stl_algobase.h:232:56: error: macro "min" passed 3 arguments, but takes just 2 /usr/include/c++/4.4/bits/stl_algobase.h:253:56: error: macro "max" passed 3 arguments, but takes just 2 In file included from /usr/include/c++/4.4/bits/stl_algo.h:61, from /usr/include/c++/4.4/algorithm:62, from test.cpp:3: /usr/include/c++/4.4/bits/algorithmfwd.h:353:41: error: macro "max" passed 3 arguments, but takes just 2 /usr/include/c++/4.4/bits/algorithmfwd.h:364:41: error: macro "min" passed 3 arguments, but takes just 2 In file included from /usr/include/c++/4.4/algorithm:61, from test.cpp:3: /usr/include/c++/4.4/bits/stl_algobase.h:186: error: expected unqualified-id before ‘const’ /usr/include/c++/4.4/bits/stl_algobase.h:186: error: expected ‘)’ before ‘const’ /usr/include/c++/4.4/bits/stl_algobase.h:186: error: expected ‘)’ before ‘const’ /usr/include/c++/4.4/bits/stl_algobase.h:186: error: expected initializer before ‘const’ /usr/include/c++/4.4/bits/stl_algobase.h:209: error: expected unqualified-id before ‘const’ /usr/include/c++/4.4/bits/stl_algobase.h:209: error: expected ‘)’ before ‘const’ /usr/include/c++/4.4/bits/stl_algobase.h:209: error: expected ‘)’ before ‘const’ /usr/include/c++/4.4/bits/stl_algobase.h:209: error: expected initializer before ‘const’ /usr/include/c++/4.4/bits/stl_algobase.h:232: error: ‘std::min’ declared as an ‘inline’ variable /usr/include/c++/4.4/bits/stl_algobase.h:232: error: template declaration of ‘const _Tp& std::min’ /usr/include/c++/4.4/bits/stl_algobase.h:235: error: expected primary-expression before ‘if’ /usr/include/c++/4.4/bits/stl_algobase.h:235: error: expected ‘}’ before ‘if’ /usr/include/c++/4.4/bits/stl_algobase.h:237: error: expected unqualified-id before ‘return’ /usr/include/c++/4.4/bits/stl_algobase.h:253: error: ‘max’ declared as an ‘inline’ variable /usr/include/c++/4.4/bits/stl_algobase.h:253: error: template declaration of ‘const _Tp& max’ /usr/include/c++/4.4/bits/stl_algobase.h:256: error: expected primary-expression before ‘if’ /usr/include/c++/4.4/bits/stl_algobase.h:256: error: expected ‘}’ before ‘if’ /usr/include/c++/4.4/bits/stl_algobase.h:258: error: expected unqualified-id before ‘return’ /usr/include/c++/4.4/bits/stl_algobase.h:259: error: expected declaration before ‘}’ token

I think that there's some name conflict between my_global.h and algorithm, so I wrap my_global.h in a namespace:

// File test.cpp
namespace MYSQL_NAMESPACE {
    #include <my_global.h>
}
#include <algorithm>
int main()
{
    return 0;
}

But it doesn't help, the compiler still report the same errors. Then I change the include order as following:

// File test.cpp
#include <algorithm>
#include <my_global.h>
int main()
{
    return 0;
}

Every thing goes well now.

Does Anybody Really Know What The Problem It Is?

TKS!

Upvotes: 3

Views: 2725

Answers (3)

user500944
user500944

Reputation:

Apparently the namespace trick does not work because min/max are macros and the preprocessor does not look at namespace scope.

This might fix the problem:

#include <my_global.h>
#undef min
#undef max
#include <algorithm>

The whole thing looks horrible though :)

Upvotes: 3

Michael Ekstrand
Michael Ekstrand

Reputation: 29100

It looks like my_global.h defines some name used by algorithm as a preprocessor macro, causing compilation to fail. With the ordering that works, you won't be able to use whatever it is that my_global.h clobbers, but your code will at least compile unless you need that feature. Since preprocessor macros are not namespaced, the namespace wrapping will not help, as you have observed.

Therefore, it sounds like my_global.h is broken, but if everything works just use the include order that works and go with it. That's my preferred include order anyway - standard library headers first, followed by external library headers, followed by internal headers.

Upvotes: 0

Mark Byers
Mark Byers

Reputation: 838896

It seems that the mysql header defines a macro min. 

#if !defined(max)
#define max(a, b)       ((a) > (b) ? (a) : (b))
#define min(a, b)       ((a) < (b) ? (a) : (b))
#endif

This has been reported to MySQL as bug 28184. The bug is marked as closed, so try updating to the newest version. According to the bug page it should be fixed in version 5.1.23, version 6.0.4 and newer versions.

Upvotes: 8

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