Q34668: Initialization of auto Arrays, Structs, Unions Not Allowed

Article: Q34668
Product(s): See article
Version(s): 4.00 5.00 | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 17-AUG-1989

Problem:

Both the ANSI draft standard for C (May 1988) and "The C Programming
Language," Second Edition (by Kernighan and Ritchie) show that
initializing aggregate data items declared with auto storage class is
allowed in Standard C; however, our compiler flags fatal errors when
such attempts are made.

The error message C2073 cannot initialize array if function is issued
when attempting to compile an array initilization within a function
such as the following:

foo() {
    char array[]="intialized local array will cause an error";
}

Response:

This restriction is stated in the "Microsoft C 5.1 Optimizing Compiler
Language Reference" on Page 89.

One possible workaround is to use the static storage class rather than
auto (auto is the default for declarations inside a function). This
process has the advantage of making only one copy of the array and
initializing it only ONCE, conceptually at the start of program
execution; however, this can be a problem for recursive functions that
may need a separate copy of the array for each invocation of the
function.

Another workaround is to declare two arrays: one static and one auto.
Initialize the static array and copy it into the auto array (e.g.
using the fast memcpy function) at the beginning of the function. Note
that there is no speed or space penalty for this process because the
second workaround is basically what the compiler would have to do if
it allowed initialization of auto arrays.

The first workaround will give a savings of both time and space over
both the second workaround and over initializing an auto aggregate.

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