All RTL routines have a C language binding: every routine has an entry point that uses C-style arguments and calling sequences. All portable C language programs use the C language interface to the RTL.
The C-language routines are named similarly to the old (now FORTRAN-style) routines, but start with a “ z” instead of “ x”. For example, instead of calling xvwrit or xlget, a C program would now call zvwrit or zlget.
The standard C definitions for each of the VICAR pixel data types are listed. See Table 4: C Declarations for Pixel Types. The data types that may be passed into the RTL, and the C declarations for each type, are listed in Table 6: C Declarations for Run-Time Library Arguments.(below)
|
Pixel
Type
|
C
Declaration
|
|
BYTE
|
unsigned
char
|
|
HALF
|
short
int
|
|
FULL
|
int
|
|
REAL
|
float
|
|
DOUB
|
double
|
|
COMP
|
struct
complex {float r, i; \};
|
Table 4: C Declarations for Pixel Types
|
RTL
Argument Type
|
C
Declaration
|
|
integer
|
int
|
|
string
|
char
x[n]
|
|
value
|
int,
char x[n], float, or double
|
|
integer
array
|
int
x[m]
|
|
string
array
|
char
x[m][n]
|
|
value
array
|
array
of any “ value” type above
|
|
pixel
buffer
|
pointer
to any pixel type.
See
Table 4: C Declarations for Pixel Types
|
|
FORTRAN
string
|
char
*x
|
|
FORTRAN
string array
|
char
*x
|
|
void
pointer
|
void
*x (actually, a pointer to anything)
|
|
pixel
pointer
|
address
of pointer to any pixel type.
See
Table 4: C Declarations for Pixel Types
|
|
pointer
to string array
|
char
**x
|
Table 6: C Declarations for Run-Time Library Arguments
Because labels and parameters can have more than one value, the routines that deal with them must be able to accept (or output) arrays of strings. The RTL expects all arrays of strings to be two-dimensional arrays of “char”. This does not mean an array of pointers to strings, but a pointer to an area of memory n*m bytes long, where n is the maximum size of each string and m is the number of strings. The inner dimension, n, must be passed in to the routine so it knows how to access the string array.
All RTL routines that use string arrays have a way to specify the length. The length is the size of the inner dimension; it is not the length of any particular string, but must include space for the null terminator at the end of a string. For example, if a string has at most 10 characters, make sure the length is at least 11 to allow room for the null terminator.