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Hi, Santos wrote in
http://groups.google.com/group/comp....ivers&lnk=nl&:

> What you do when a function has failed will obviously be highly
> dependant on the exact situation, but for small test programs (like
> yours) you might want to print a useful message printing what went
> wrong and where (function and source line number) and probably, exit.
> Recovery strategies (even if they are possible) may be too advanced at
> this point.
>
> An example:
>
> if (fscanf(file, "%d", &i) != 1) {
> fprintf(stderr, "%s (%d): fscanf() failed.\n",
> __FILE__, __LINE__);
> exit(EXIT_FAILURE);
> }
>
> With C99 you can also use the predefined identifier __func__ to extract
> the name of the current function (as a string).

> For checking the internal consistency of the program you can use the
> macro assert in assert.h. If the expression passed to assert evaluates
> to zero (logically false), assert will print a message and abort the
> program. You can define the macro NDEBUG *prior* to including assert.h
> to turn off all assertions.
>
> Many library functions also set the object 'errno' to some integer value
> upon failure. To use this mechanism you need to include the header
> errno.h and set errno to zero before the function in question is
> called. Immediately after you need to check errno for the presence of
> documented error values (like ERANGE, EDOM, EILSEQ and other
> implementation defined values), and if so, take appropriate action. You
> can translate the error codes in errno to implementation specific
> messages using the strerror or perror.

What do ERANGE, EDOM, EILSEQ represent and how do I 'check errno for
the presence of [these] document error values'?

Albert wrote:

> What do ERANGE, EDOM, EILSEQ represent and how do I 'check errno for
> the presence of [these] document error values'?

The identifiers represent the three macros defined in <errno.h> for
standard values for errno. Any elementary C text should provide
explanation. In short:

EDOM means there is a domain error; that is, the space over which the
function is defined does not include the argument. [Example: sqrt(-1)]

ERANGE means there is a range error; that is, even though the
mathematical function is defined for the argument, the result is not
representable in the return type. [example: exp(DBL_MAX)]

EILSEQ means there is an encoding error when translating a multibyte
character sequence.

How you check for these is covered in any elementary C text. An example:

#include <errno.h>
#include <math.h>
#include <stdio.h>

int main(void)
{
double x = -1, y;
errno = 0;
y = sqrt(x);
switch (errno)
{
case 0: printf("sqrt(%g) = %g\n", x, y);
break;
case EDOM:
printf("sqrt() is not defined for argument %g\n", x);
errno = 0;
break;
case ERANGE:
printf("sqrt(%g) is mathematically defined, but\n"
"its result is not representable in a double.\n",
x);
errno = 0;
break;
default:
printf("sqrt(%g) returned the implementation-defined\n"
"errno of %d. Check the implementation documentation\n"
"for clarification.\n", x, errno);
errno = 0;
break;
}
return 0;
}