Vax C90-EL SERIES Service Manual download pdf (Page 147)

Interlanguage Communication [9]

9.3.2 Argument Passing

Because Fortran subroutines expect arguments to be passed by pointers rather

than by value, C and C++ functions called from Fortran subroutines must pass

pointers rather than values.

All argument passing in Cray Standard C is strictly by value. To prepare for a

function call between two Cray Standard C functions, a copy is made of each

actual argument. A function can change the values of its formal parameters, but

these changes cannot affect the values of the actual arguments. It is possible,

however, to pass a pointer. (All array arguments are passed by this method.) This

capability is analogous to the Fortran method of passing arguments.

In addition to passing by value, Cray Standard C++ also provides passing by

reference.

9.3.3 Array Storage

C and C++ arrays are stored in memory in row-major order; and Fortran arrays

are stored in memory in column-major order. For example, the C or C++ array

declaration int A[3][2] is stored in memory as:

A[0][0] A[0][1]

A[1][0] A[1][1]

A[2][0] A[2][1]

The previously defined array is viewed linearly in memory as:

A[0][0] A[0][1] A[1][0] A[1][1] A[2][0] A[2][1]

The Fortran array declaration INTEGER A(3,2) is stored in memory as:

A(1,1) A(2,1) A(3,1)

A(1,2) A(2,2) A(3,2)

The previously defined array is viewed linearly in memory as:

A(1,1) A(2,1) A(3,1) A(1,2) A(2,2) A(3,2)

When an array is shared between Cray Standard C, C++, and Fortran, its

dimensions are declared and referenced in C and C++ in the opposite order in

S–2179–36 127

1 2 ... 142 143 144 145 146 147 148 149 150 151 152 ... 215 216

No comments

Vax C90-EL SERIES Service Manual Page 147