Corresponding Data Types

The following table shows the correspondence between the data types available in IBM C/C++ Compilers, C Set ++ for AIX, Fortran, and Pascal. Several data types in C have no equivalent representation in Pascal or Fortran. Do not use them when programming for interlanguage calls. Blank table cells indicate that no matching data type exists.

C and C++ Data Types	Fortran Data Types	Pascal Data Types
Correspondence of Data Types among C, C++, Fortran, and Pascal
char	CHARACTER	CHAR
signed char	INTEGER*1 BYTE	PACKED -128..127
unsigned char	LOGICAL*1	PACKED 0..255
signed short int	INTEGER*2	PACKED -32768..32767
unsigned short int	LOGICAL*2	PACKED 0..65535
signed long int	INTEGER*4	INTEGER
unsigned long int	LOGICAL*4	--
signed long long int	INTEGER*8	--
unsigned long long int	LOGICAL*8	--
float	REAL REAL*4	SHORTREAL
double	REAL*8 DOUBLE PRECISION	REAL
long double	REAL*8 DOUBLE PRECISION	REAL
long double (with -qlongdouble or -qldbl128)	REAL*16	--
structure of two floats	COMPLEX COMPLEX*4	RECORD of two SHORTREALS
structure of two doubles	COMPLEX*16 DOUBLE COMPLEX	RECORD of two REALS
structure of two long doubles	COMPLEX*16	--
struct	--	RECORD (see notes below)
enumeration	INTEGER*4	Enumeration
char[n]	CHARACTER*n	PACKED ARRAY[1..n] OF CHAR
array pointer (*) to type	Dimensioned variable (transposed)	ARRAY
pointer (*) to function	Functional Parameter	Functional Parameter
structure (with -qalign=pack)	Sequence derived type	PACKED RECORD

Special Treatment of Character and Aggregate Data
Most numeric data types have counterparts across the three languages. Character and aggregate data types require special treatment:

Because of padding and alignment differences, C structures do not exactly correspond to the Pascal RECORD data type.
C character strings are delimited by a '\0'character. In Fortran, all character variables and expressions have a length that is determined at compile time. If Fortran passes a string argument to another routine, it adds a hidden argument giving the length to the end of the argument list. This length argument must be explicitly declared in C. The C code should not assume a null terminator; the supplied or declared length should always be used. Use the strncat, strncpm, and strncpy functions of the C runtime library. These functions are described in the AIX Version 4 Technical Reference, Volumes 1 and 2: Base Operating System and Extensions.
Pascal's STRING data type corresponds to a C structure For example.:
```
    VAR s: STRING(10);
```
is equivalent to:
```
    struct {
        int length;
        char str [10];
    };
```
where length contains the actual length of STRING.
The -qmacpstr option converts Pascal string literals into null-terminated strings, where the first byte contains the length of the string. See macpstr for a description of this option.

C and Pascal store array elements in row-major order (array elements in the same row occupy adjacent memory locations). Fortran stores array elements in ascending storage units in column-major order (array elements in the same column occupy adjacent memory locations). The following example shows how a two-dimensional array declared by A[3][2] in C, A[1..3,1..2] in Pascal, and by A(3,2) in Fortran, is stored:

Storage Unit	C and C++ Element Name	Pascal Element Name	Fortran Element Name
Storage of a Two-Dimensional Array
Lowest	A[0][0]	A[1,1]	A(1,1)
	A[0][1]	A[1,2]	A(2,1)
	A[1][0]	A[2,1]	A(3,1)
	A[1][1]	A[2,2]	A(1,2)
	A[2][0]	A[3,1]	A(2,2)
Highest	A[2][1]	A[3,2]	A(3,2)

In general, for a multidimensional array, if you list the elements of the array in the order they are laid out in memory, a row-major array will be such that the rightmost index varies fastest, while a column-major array will be such that the leftmost index varies fastest.

Interlanguage Calling Conventions
Using the Subroutine Linkage Conventions in Interlanguage Calls
Sample Program: C Calling Fortran