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68 lines
2.1 KiB
Markdown
68 lines
2.1 KiB
Markdown
---
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icon: cpu
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title: Write C Bindings
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order: 18
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---
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In order to use a C/C++ library in python, you need to write bindings for it.
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pkpy uses an universal signature to wrap a C function pointer as a python function or method, i.e `py_CFunction`.
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```c
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typedef bool (*py_CFunction)(int argc, py_Ref argv);
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```
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+ `argc` is the number of arguments passed to the function.
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+ `argv` is the pointer to the first argument.
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If successful, the function should return `true` and set the return value in `py_retval()`. In case there is no return value, you should use `py_newnone(py_retval())`.
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If an error occurs, the function should raise an exception and return `false`.
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## Steps
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Say you have a function `add` that takes two integers and returns their sum.
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```c
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int add(int a, int b) {
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return a + b;
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}
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```
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Here is how you can write the binding for it:
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```c
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// 1. Define a wrapper function with the signature `py_CFunction`.
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bool py_add(int argc, py_Ref argv) {
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// 2. Check the number of arguments.
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PY_CHECK_ARGC(2);
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// 3. Check the type of arguments.
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PY_CHECK_ARG_TYPE(0, tp_int);
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PY_CHECK_ARG_TYPE(1, tp_int);
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// 4. Convert the arguments into C types.
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int _0 = py_toint(py_arg(0));
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int _1 = py_toint(py_arg(1));
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// 5. Call the original function.
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int res = add(_0, _1);
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// 6. Set the return value.
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py_newint(py_retval(), res);
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// 7. Return `true`.
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return true;
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}
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```
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Once you have the wrapper function, you can bind it to a python module via `py_bindfunc`.
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```c
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py_GlobalRef mod = py_getmodule("__main__");
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py_bindfunc(mod, "add", py_add);
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```
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Alternatively, you can use `py_bind` with a signature, which allows you to specify some default values.
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```c
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py_GlobalRef mod = py_getmodule("__main__");
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py_bind(mod, "add(a, b=1)", py_add);
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```
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See also:
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+ [`py_bind`](/c-api/functions/#py_bind)
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+ [`py_bindmethod`](/c-api/functions/#py_bindmethod)
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+ [`py_bindfunc`](/c-api/functions/#py_bindfunc)
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+ [`py_bindproperty`](/c-api/functions/#py_bindproperty)
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+ [`py_newmodule`](/c-api/functions/#py_newmodule)
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+ [`py_newtype`](/c-api/functions/#py_newtype) |