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Top Forums Programming Some questions regarding old if.c Post 302930452 by ongoto on Sunday 4th of January 2015 09:09:33 AM
Old 01-04-2015
Quote:
Code:
if (exp()) is asking if the function exists; it's not calling that function.
...

I think there's a good chance that code that you identified actually does make the call to exp(), with unknown data on the stack. I think to just check if the function exists, the code would be if ( exp ) .
That is possible. I can't remember all the type checking details used in those days either. One way Bash (nowadays) distinguises between a variable named 'func' and a function named 'func()' is the parentheses. But that may not have been true 20 years ago in the C language.

Last edited by ongoto; 01-04-2015 at 10:34 AM..
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exp(3M) 						  Mathematical Library Functions						   exp(3M)

NAME
exp, expf, expl - exponential function SYNOPSIS
cc [ flag... ] file... -lm [ library... ] #include <math.h> double exp(double x); float expf(float x); long double expl(long double x); DESCRIPTION
These functions compute the base-e exponential of x. RETURN VALUES
Upon successful completion, these functions return the exponential value of x. If the correct value would cause overflow, a range error occurs and exp(), expf(), and expl() return HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively. If x is NaN, a NaN is returned. If x is +-0, 1 is returned. If x is +Inf, x is returned. For exceptional cases, matherr(3M) tabulates the values to be returned by exp() as specified by SVID3 and XPG3. See standards(5). ERRORS
These functions will fail if: Range Error The result overflows. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the overflow floating-point exception is raised. The exp() function sets errno to ERANGE if the result overflows. USAGE
An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions. An application can also set errno to 0 before calling exp(). On return, if errno is non-zero, an error has occurred. The expf() and expl() functions do not set errno. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
feclearexcept(3M), fetestexcept(3M), isnan(3M), log(3M), math.h(3HEAD), matherr(3M), mp(3MP), attributes(5), standards(5) SunOS 5.10 1 Nov 2003 exp(3M)
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