Q11876: C 5.00/5.10 Give "Constant Too Large" with Decimal Initializer

Article: Q11876
Product(s): See article
Version(s): 3.00 4.00 5.00 5.10 | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 6-FEB-1991

Problem:

When I attempt to use the most negative long integer, my results
depend on whether I used decimal or hexadecimal to enter the value.
The results also seem to vary between C version 5.00 and the newer
compilers.

For example, the following program produces the compiler warning
"constant too big" when compiled with C 5.00:

long d1, d2;

void main(void)
{
    long  d1 = -2147483648L;
    long  d2 =  0x80000000;
    printf("d1 = %ld", d1);
    printf("d2 = %ld", d2);
}

The compiler assigns the value -2147483647 to d1, although it assigns
-2147483648 to d2. The internal representation of d1 seems incorrect.

Response:

In C versions 5.00 and earlier, the decimal constant -2147483648L is
treated semantically as a unary minus sign applied to a positive
constant, 2147483648L. The positive constant is outside the valid
range for constants, and therefore, is reduced to the maximum positive
long integer; thus, the message "constant too large" is issued.

On the other hand, the hexadecimal constant 0x80000000 is treated
semantically as a series of bits. It has few enough bits to fit into a
long integer, so no message is issued. Had the constant contained too
many bits to fit into a long integer, it too would have been reduced
to 2^31 - 1.

C version 5.10 does not complete compilation in this situation and
halts with the error, "C2177: constant too large." This ensures that
you will not be using an unexpected value.

Beginning with C version 6.00, long constants can be initialized to
decimal values larger than MAX_LONG (as per the ANSI draft standard),
so this is no longer a problem at compilation time.

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