104 lines
2.3 KiB
Groff
104 lines
2.3 KiB
Groff
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.Dd February 15, 2008
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.Dt ffi_call 3
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.Sh NAME
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.Nm ffi_call
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.Nd Invoke a foreign function.
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.Sh SYNOPSIS
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.In ffi.h
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.Ft void
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.Fo ffi_call
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.Fa "ffi_cif *cif"
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.Fa "void (*fn)(void)"
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.Fa "void *rvalue"
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.Fa "void **avalue"
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.Fc
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.Sh DESCRIPTION
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The
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.Nm ffi_call
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function provides a simple mechanism for invoking a function without
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requiring knowledge of the function's interface at compile time.
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.Fa fn
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is called with the values retrieved from the pointers in the
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.Fa avalue
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array. The return value from
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.Fa fn
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is placed in storage pointed to by
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.Fa rvalue .
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.Fa cif
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contains information describing the data types, sizes and alignments of the
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arguments to and return value from
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.Fa fn ,
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and must be initialized with
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.Nm ffi_prep_cif
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before it is used with
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.Nm ffi_call .
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.Pp
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.Fa rvalue
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must point to storage that is sizeof(ffi_arg) or larger for non-floating point
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types. For smaller-sized return value types, the
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.Nm ffi_arg
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or
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.Nm ffi_sarg
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integral type must be used to hold
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the return value.
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.Sh EXAMPLES
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.Bd -literal
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#include <ffi.h>
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#include <stdio.h>
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unsigned char
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foo(unsigned int, float);
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int
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main(int argc, const char **argv)
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{
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ffi_cif cif;
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ffi_type *arg_types[2];
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void *arg_values[2];
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ffi_status status;
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// Because the return value from foo() is smaller than sizeof(long), it
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// must be passed as ffi_arg or ffi_sarg.
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ffi_arg result;
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// Specify the data type of each argument. Available types are defined
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// in <ffi/ffi.h>.
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arg_types[0] = &ffi_type_uint;
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arg_types[1] = &ffi_type_float;
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// Prepare the ffi_cif structure.
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if ((status = ffi_prep_cif(&cif, FFI_DEFAULT_ABI,
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2, &ffi_type_uint8, arg_types)) != FFI_OK)
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{
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// Handle the ffi_status error.
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}
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// Specify the values of each argument.
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unsigned int arg1 = 42;
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float arg2 = 5.1;
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arg_values[0] = &arg1;
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arg_values[1] = &arg2;
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// Invoke the function.
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ffi_call(&cif, FFI_FN(foo), &result, arg_values);
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// The ffi_arg 'result' now contains the unsigned char returned from foo(),
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// which can be accessed by a typecast.
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printf("result is %hhu", (unsigned char)result);
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return 0;
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}
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// The target function.
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unsigned char
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foo(unsigned int x, float y)
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{
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unsigned char result = x - y;
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return result;
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}
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.Ed
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.Sh SEE ALSO
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.Xr ffi 3 ,
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.Xr ffi_prep_cif 3
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