1 .Dd February 15, 2008 2 .Dt ffi_call 3 3 .Sh NAME 4 .Nm ffi_call 5 .Nd Invoke a foreign function. 6 .Sh SYNOPSIS 7 .In ffi.h 8 .Ft void 9 .Fo ffi_call 10 .Fa "ffi_cif *cif" 11 .Fa "void (*fn)(void)" 12 .Fa "void *rvalue" 13 .Fa "void **avalue" 14 .Fc 15 .Sh DESCRIPTION 16 The 17 .Nm ffi_call 18 function provides a simple mechanism for invoking a function without 19 requiring knowledge of the function's interface at compile time. 20 .Fa fn 21 is called with the values retrieved from the pointers in the 22 .Fa avalue 23 array. The return value from 24 .Fa fn 25 is placed in storage pointed to by 26 .Fa rvalue . 27 .Fa cif 28 contains information describing the data types, sizes and alignments of the 29 arguments to and return value from 30 .Fa fn , 31 and must be initialized with 32 .Nm ffi_prep_cif 33 before it is used with 34 .Nm ffi_call . 35 .Pp 36 .Fa rvalue 37 must point to storage that is sizeof(long) or larger. For smaller 38 return value sizes, the 39 .Nm ffi_arg 40 or 41 .Nm ffi_sarg 42 integral type must be used to hold 43 the return value. 44 .Sh EXAMPLES 45 .Bd -literal 46 #include <ffi/ffi.h> 47 #include <stdio.h> 48 49 unsigned char 50 foo(unsigned int, float); 51 52 int 53 main(int argc, const char **argv) 54 { 55 ffi_cif cif; 56 ffi_type *arg_types[2]; 57 void *arg_values[2]; 58 ffi_status status; 59 60 // Because the return value from foo() is smaller than sizeof(long), it 61 // must be passed as ffi_arg or ffi_sarg. 62 ffi_arg result; 63 64 // Specify the data type of each argument. Available types are defined 65 // in <ffi/ffi.h>. 66 arg_types[0] = &ffi_type_uint; 67 arg_types[1] = &ffi_type_float; 68 69 // Prepare the ffi_cif structure. 70 if ((status = ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 71 2, &ffi_type_uint8, arg_types)) != FFI_OK) 72 { 73 // Handle the ffi_status error. 74 } 75 76 // Specify the values of each argument. 77 unsigned int arg1 = 42; 78 float arg2 = 5.1; 79 80 arg_values[0] = &arg1; 81 arg_values[1] = &arg2; 82 83 // Invoke the function. 84 ffi_call(&cif, FFI_FN(foo), &result, arg_values); 85 86 // The ffi_arg 'result' now contains the unsigned char returned from foo(), 87 // which can be accessed by a typecast. 88 printf("result is %hhu", (unsigned char)result); 89 90 return 0; 91 } 92 93 // The target function. 94 unsigned char 95 foo(unsigned int x, float y) 96 { 97 unsigned char result = x - y; 98 return result; 99 } 100 .Ed 101 .Sh SEE ALSO 102 .Xr ffi 3 , 103 .Xr ffi_prep_cif 3 104
