HP 3000 Manuals HP 3000 Manuals
EQUIVALENCE Statement (Nonexecutable) The EQUIVALENCE statement associates variables so that they share the same storage space.Semantics Function names, formal arguments, dynamic arrays, and record names must not appear in an EQUIVALENCE statement. Each array or substring subscript must be an integer constant expression. The EQUIVALENCE statement conserves storage. For example, arrays that are manipulated at different times in the same program can share the same storage space through the EQUIVALENCE statement. Thus, the same storage space is used for each array. Equivalenced data items can be of different types. As an extension to the ANSI 77 standard, character and noncharacter data items can share the same storage space through the EQUIVALENCE statement. The EQUIVALENCE statement does not cause type conversion or imply mathematical equivalence. If an array and a simple variable share the same storage space through the EQUIVALENCE statement, the array does not have the characteristics of a simple variable and the simple variable does not have the characteristics of an array. They only share the same storage space. Care should be taken when data types of different sizes share the same storage space, because the EQUIVALENCE statement specifies that each data item in a list has the same first storage unit. For example, if an INTEGER*4 variable and a REAL*8 variable share the same storage space, the integer value occupies the same space as the leftmost word of the two-word real value. Equivalence of Character Variables As an extension to the ANSI 77 standard, character and noncharacter data items can share the same storage space. Example Notes --------------------------------------------------------------------------------------- EQUIVALENCE (a,b),(c(2),d,e) The variables a and b share the same storage space; c(2), d, and e share the same storage space. Multi-Dimensioned Equivalence As an extension to the ANSI 77 standard, it is possible to indicate the element of an array with two or more dimensions by specifying its position as if it were a single dimension array. Example BYTE message (4,10) INTEGER name (10) EQUIVALENCE (name, message(1)) Memory Storage Locations for Message and Name ---------------------------------------------------------------------------------------------- | | | | | Array MESSAGE | Storage Space Byte Number | Array NAME | | | | | ---------------------------------------------------------------------------------------------- | | | | | MESSAGE(1,1) | 1 through 4 | NAME(1) | | MESSAGE(2,1) | | | | MESSAGE(3,1) | | | | MESSAGE(4,1) | | | | | | | ---------------------------------------------------------------------------------------------- | | | | | MESSAGE(1,2) | 5 through 8 | NAME(2) | | MESSAGE(2,2) | | | | MESSAGE(3,2) | | | | MESSAGE(4,2) | | | | | | | ---------------------------------------------------------------------------------------------- | | | | | MESSAGE(1,3) | 9 through 12 | NAME(3) | | MESSAGE(2,3) | | | | MESSAGE(3,3) | | | | MESSAGE(4,3) | | | | | | | ---------------------------------------------------------------------------------------------- | | | | | MESSAGE(1,4) | 13 through 16 | NAME(4) | | MESSAGE(2,4) | | | | MESSAGE(3,4) | | | | MESSAGE(4,4) | | | | | | | ---------------------------------------------------------------------------------------------- | | | | | : | : | : | | | | | ---------------------------------------------------------------------------------------------- | | | | | MESSAGE(1,10) | 37 through 40 | NAME(10) | | MESSAGE(2,10) | | | | MESSAGE(3,10) | | | | MESSAGE(4,10) | | | | | | | ----------------------------------------------------------------------------------------------
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