alnsn / nupy

Expose C/C++ structs to numpy

Nupy C/C++ Library

Expose C/C++ structs to numpy

SYNOPSIS

#define nupyStruct(T) begin a declaration of struct T

#define nupyEnd() end a declaration

#define nupyBase(T) declare a base class T - C++ only

#define nupyM(M) declare a member M

#define nupyFAM(M) declare flexible array member M

DESCRIPTION

Nupy is a simple set of C++ macros to generate a dtype string for a class or a struct.

For example, C/C++ struct Line

struct Line
{
        double start[2];
        double end  [2];
        char   note [16];
};

can be "decorated" by nupyStruct(Line) and nupyEnd() macros and all members can be wrapped by nupyM(m)

struct Line
{
        nupyStruct(Line)

        double nupyM(start) [2];
        double nupyM(end  ) [2];
        char   nupyM(note ) [16];

        nupyEnd()
};

In plain C nupyStruct(T) and nupyEnd() evaluate to nothing and nupyM(M) evaluates to M producing a struct identical to the original.

In C++, the second definition generates nupy_dtype static member function

int Line::nupy_dtype(const char* str, size_t bufsz, size_t famsz = 0);

If bufsz is big enough, the function copies Line's dtype to buf producing a string similar to

"[('start','<f8',(2)),('end','<f8',(2)),('note','|S16')]"

A call to nupy_dtype(buf, bufsz) is equivalent to snprintf call

snprintf(buf, bufsz, "%s", dtypestr);

except that snprintf can be called multiple times.

In fact, nupy_dtype uses only snprintf from -lc. All other dependencies are C++ metaprogramming stuff.

No padding between members or at the end are allowed. If there is a mismatch between a total size of members wrapped by nupyM(M) and a size of a struct, compile-time assert will be triggered.

Class inheritance is supported with nupyBase(T). There is no compile-time check to detect a wrong order of nupyBase(T) for a class with multiple bases.

Only one member declaration per line is allowed.

Compile-time complexity of C++ code is proportional to a number of members and it also increases as a distance between nupyStruct(T) and nupyEnd() increases (even lines with comments count!). You may need to change a default value of template depth to compile big structs.

REQUIREMENTS

You need a decent C++ compiler that works with boost and that supports __typeof__.

DEPENDENCIES

The library is header-only. It depends on the following boost libraries (all header-only)

• enable_if
• mpl
• preprocessor
• type_traits

SEE ALSO

snprintf(3)

BUGS

At the moment, the library does not support big endian architectures.

AUTHOR

Alexander Nasonov