HP aC++/HP C Programmer's Guide (B3901-90036; A.06.26; September 2011)

union u1 { // OK

char c[4];

int v;

char dummy; };

Another type of warning is on the use of IO functions that read/write persistent data

from files that may be endian-dependent:

read(0, &i, sizeof(i));

fread(&ai[0], sizeof(int), elems_of(ai, int), stdin);

write(1, &i, sizeof(i));

fwrite(&ai[0], sizeof(int), elems_of(ai, int), stdout);

This warning can be suppressed by adding an extra cast:

fread((char*)(void*)ai, sizeof(char), 1, stdin); // OK

Another +wendian warning captures cases where a cast when later dereferenced can

cause endian issues.

Preprocessor Options

The following options are accepted by the preprocessor:

-C

Using the -C option prevents the preprocessor from stripping comments. See the

description of cpp in the cpp(1) manpage for details.

-dM

When -dM is present, instead of normal preprocessor output the compiler lists the

#define directives it encounters as it preprocesses the file, thus providing a list of all

macros that are in effect at the start of the compilation. The -dM option requires that -P

or -E also be specified.

A common use of this option is to determine the compiler's predefined macros. For

example:

touch foo.c ; cc -E -dM foo.c

-Dname

-Dname[=def]

name is the symbol name that is defined for the preprocessor.

def is the definition of the symbol name (name).

The -Dname option defines a symbol name (name) to the preprocessor, as if defined by

the preprocessing directive#define.

Preprocessor Options 87