Corresponding Data Types

The following table shows the correspondence between the data types available in C/C++, 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.

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 of a Two-Dimensional Array
  Storage Unit	C and C++ Element Name	Pascal Element Name	Fortran Element Name
  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
Use the Subroutine Linkage Conventions in Interlanguage Calls
Sample Program: C Calling Fortran