C/C++ Programmer's Guide (G06.27+, H06.08+, J06.03+)

If variable definitions are desired to be in the C++ source, remove the extern specifier and
change the pTAL source to ?NOEXPORTGLOBALS.
Parameters and Variables
This subsection provides guidelines for declaring compatible pTAL and C variables and parameters.
These guidelines supplement those given in Sharing Data (page 130). The topics discussed are:
• STRING and char Variables
• Arrays (page 134)
• Structures (page 135)
• Multidimensional Arrays (page 135)
• Arrays of Structures (page 136)
• Redefinitions and Unions (page 136)
• Pointers (page 136)
• Enumeration Variables (page 137)
• pTAL Routines as Parameters to C (page 138)
• C Routines as Parameters to pTAL (page 138)
STRING and char Variables
pTAL STRING and C char simple variables each occupies one byte of a word. Share variables of
type pTAL STRING and C char by using pointers or declare both as int.
Arrays
pTAL and C arrays differ:
C ArraypTAL ArrayCharacteristic
Always zeroAny integerLower bound
One or more dimensionsOne dimension *Dimensions
Indirect onlyDirect or indirectDirect or indirect
Native C and C++ only have byte
addressing
STRING arrays and extended indirect
arrays are byte addressed; all other
arrays are word addressed
Byte or word addressing
* pTAL structures can emulate multidimensional C arrays, as discussed in Multidimensional Arrays (page 135).
To declare compatible pTAL and C arrays:
• Use data types and alignments that satisfy both compilers.
• Declare pTAL arrays that have a lower bound of 0.
• Declare one-dimensional C arrays.
• Declare indirect pTAL arrays.
These are compatible arrays in pTAL and native C:
pTAL Code C Code
INT .EXT robin[0:9]; short robin [10];
INT(32) .EXT gull[0:14]; long gull [15];
STRING .EXT grebe[0:9]; char grebe [10];
134 Mixed-Language Programming for TNS/R and TNS/E Native Programs