Q66217: Pascal Modifier Might Generate Bogus Warning C4059

Article: Q66217
Product(s): See article
Version(s): 6.00   | 6.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | buglist6.00 | mspl13_c
Last Modified: 24-OCT-1990

In certain cases, the use of the Pascal modifier on a function will
generate the following warning incorrectly:

   test.c(18): warning C4059: segment lost in conversion

The following code, when compiled using "cl /W2 /c test.c" will
generate the C4059 warning:

Code Example
------------

#include <stdio.h>

struct s {int i,j,k,l; };

struct s Pascal foo(void)
{
struct s b = {1, 2, 3, 4};

    return b;
}

void foobar(struct s b)
{
    printf("%d %d %d %d\n", b.i, b.j, b.k, b.l);
}

void main () {
   foobar(foo());              /* this line causes warning C4059 */
}

This warning should not be generated for the above code. The problem
occurs if you call a function that takes a structure as an argument
with a procedure that returns a structure and is declared with the
Pascal modifier, as in the above example. The problem does not occur
with C 5.10.

Although the warning is intended to flag a possible problem, the
warning is not valid and the compiler generates the correct code in
the above situation. Note that the code is incorrect only if /Au or
/Aw are used.

The warning goes away if you do one of the following:

1. Compile with the /qc option. This uses the quick compiler rather
   than the full optimizing compiler.

2. Remove the Pascal modifier from line 3.

3. Compile in compact or large memory models (/AC or /AL).

Microsoft has confirmed this to be a problem with C version 6.00. We
are researching this problem and will post new information here as it
becomes available.

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