Intel(R) Fortran Compiler for Linux* Systems User's Guide Volume I ...

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Intel® Fortran Compiler for Linux* Systems User's Guide Volume I: Building Applications External variables are case-sensitive, so the cases must be matched between different languages, as discussed in the section on naming conventions. Common external data exchange is described in the following sections: • Using Global Variables • Using Fortran Common Blocks and C Structures Using Global Variables in Mixed-Language Programming A variable can be shared between Fortran and C by declaring it as global (or COMMON) in one language and accessing it as an external variable in the other language. In Fortran programs, variables must be passed as arguments. In Fortran, a variable can access a global parameter by using the EXTERN option for ATTRIBUTES. For example: !DEC$ ATTRIBUTES C, EXTERN :: idata INTEGER idata (20) EXTERN tells the compiler that the variable is actually defined and declared global in another source file. If Fortran declares a variable external with EXTERN, the language it shares the variable with must declare the variable global. In C, a variable is declared global with the statement: int idata[20]; // declared as global (outside of any function) Fortran can declare the variable global (COMMON) and other languages can reference it as external: ! Fortran declaring PI global REAL PI COMMON /PI/ PI ! Common Block and variable have the same name In C, the variable is referenced as an external with the statement: //C code with external reference to PI0 extern float PI; 194
Intel® Fortran Compiler for Linux* Systems User's Guide, Volume I: Building Applications Note that the global name C references is the name of the Fortran common block, not the name of a variable within a common block. Thus, you cannot use blank common to make data accessible between C and Fortran. In the preceding example, the common block and the variable have the same name, which helps keep track of the variable between the two languages. Obviously, if a common block contains more than one variable they cannot all have the common block name. (See Using Fortran Common Blocks and C Structures.) Using Fortran Common Blocks and C Structures To reference C structures from Fortran common blocks and vice versa, you must take into account the way the common blocks and structures differ in their methods of storing member variables in memory. Fortran places common block variables into memory in order as close together as possible, with the following rules: • A single BYTE, INTEGER(1), LOGICAL(1), or CHARACTER variable in common block list begins immediately following the previous variable or array in memory. • All other types of single variables begin at the next even address immediately following the previous variable or array in memory. • All arrays of variables begin on the next even address immediately following the previous variable or array in memory, except for CHARACTER arrays which always follow immediately after the previous variable or array. • All common blocks begin on a four-byte aligned address. Because of these padding rules, you must consider the alignment of C structure elements with Fortran common block elements and assure matching either by making all variables the same types and kinds in both languages (using only 4- byte and 8-byte data types in both languages simplifies this) or by using the C pack pragmas in the C code around the C structure to make C data packing like Fortran's. For example: #pragma pack(2) struct { int N; char INFO[30]; } examp; #pragma pack() To restore the original packing, you must add #pragma pack( ) at the end of the structure. (Remember: Fortran module data can be shared directly with C structures with appropriate naming.) 195
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Intel(R) Fortran Compiler for Linux
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Table Of Contents Table Of Contents
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Table Of Contents Predefined Prepro
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Table Of Contents -e90 or -e95 ....
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Table Of Contents -[no]fpconstant .
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Table Of Contents -noinclude ......
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Table Of Contents -par_threshold n.
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Table Of Contents Using Debugger Co
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Table Of Contents Limitations of Nu
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Table Of Contents Specifiers for Fi
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Table Of Contents Programming with
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Table Of Contents Run-Time Message
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About the Intel® Fortran Compiler
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Intel® Fortran Compiler for Linux*
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Index ! !DEC$ prefix ..............
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Index -assume dummy_aliases compile
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Index common blocks allocating ....
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Index compiler option -convert meth
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Index additional...................
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Index file information OPEN stateme
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Index FOR$IOS_FLTOVF error message
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Index FOR$IOS_TOOMANREC error messa
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Index -fvisibility-keyword compiler
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Index -ip_no_pinlining compiler opt
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Index manuals additional...........
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Index -nus compiler option.........
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Index -pad_source compiler option..
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Index record characteristics OPEN s
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Index signal routine calling ......
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Index uninstall.sh file ...........
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