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Hi I have the following function called zeroin I'd like to compile and link in with a Cpp file but I can't get past the first step of compiling the c file. The function is called zeroin.c I obtained from here. I have put the file in it's own directory, cd'd to it, and since it uses math.h I have used gcc with the -lm flag to make sure the library is linked in.
gcc -Wall -O zeroin.c -o zeroin -lm
However I get the following errors:
zeroin.C:50:15: error: 'ax' was not declared in this scope
zeroin.C:50:18: error: 'bx' was not declared in this scope
zeroin.C:50:21: error: 'f' was not declared in this scope
zeroin.C:50:23: error: 'tol' was not declared in this scope
zeroin.C:50:26: error: expression list treated as compound expression in initialiser [-fpermissive]
zeroin.C:51:1: error: expected ',' or ';' before 'double'
zeroin.C:55:1: error: expected unqualified-id before '{' token
I've included the code for the C code function below - I don't really know C very well and am only trying to compile it so as to use it to find roots for functions in a C++ file I have. How can I solve these errors?
Thanks, Ben.
#include "math.h"
double zeroin(ax,bx,f,tol) /* An estimate to the root */
double ax; /* Left border | of the range */
double bx; /* Right border| the root is seeked*/
double (*f)(double x); /* Function under investigation */
double tol; /* Acceptable tolerance */
{
double a,b,c; /* Abscissae, descr. see above */
double fa; /* f(a) */
double fb; /* f(b) */
double fc; /* f(c) */
a = ax; b = bx; fa = (*f)(a); fb = (*f)(b);
c = a; fc = fa;
for(;;) /* Main iteration loop */
{
double prev_step = b-a; /* Distance from the last but one*/
/* to the last approximation */
double tol_act; /* Actual tolerance */
double p; /* Interpolation step is calcu- */
double q; /* lated in the form p/q; divi- */
/* sion operations is delayed */
/* until the last moment */
double new_step; /* Step at this iteration */
if( fabs(fc) < fabs(fb) )
{ /* Swap data for b to be the */
a = b; b = c; c = a; /* best approximation */
fa=fb; fb=fc; fc=fa;
}
tol_act = 2*EPSILON*fabs(b) + tol/2;
new_step = (c-b)/2;
if( fabs(new_step) <= tol_act || fb == (double)0 )
return b; /* Acceptable approx. is found */
/* Decide if the interpolation can be tried */
if( fabs(prev_step) >= tol_act /* If prev_step was large enough*/
&& fabs(fa) > fabs(fb) ) /* and was in true direction, */
{ /* Interpolatiom may be tried */
register double t1,cb,t2;
cb = c-b;
if( a==c ) /* If we have only two distinct */
{ /* points linear interpolation */
t1 = fb/fa; /* can only be applied */
p = cb*t1;
q = 1.0 - t1;
}
else /* Quadric inverse interpolation*/
{
q = fa/fc; t1 = fb/fc; t2 = fb/fa;
p = t2 * ( cb*q*(q-t1) - (b-a)*(t1-1.0) );
q = (q-1.0) * (t1-1.0) * (t2-1.0);
}
if( p>(double)0 ) /* p was calculated with the op-*/
q = -q; /* posite sign; make p positive */
else /* and assign possible minus to */
p = -p; /* q */
if( p < (0.75*cb*q-fabs(tol_act*q)/2) /* If b+p/q falls in [b,c]*/
&& p < fabs(prev_step*q/2) ) /* and isn't too large */
new_step = p/q; /* it is accepted */
/* If p/q is too large then the */
/* bissection procedure can */
/* reduce [b,c] range to more */
/* extent */
}
if( fabs(new_step) < tol_act ) /* Adjust the step to be not less*/
if( new_step > (double)0 ) /* than tolerance */
new_step = tol_act;
else
new_step = -tol_act;
a = b; fa = fb; /* Save the previous approx. */
b += new_step; fb = (*f)(b); /* Do step to a new approxim. */
if( (fb > 0 && fc > 0) || (fb < 0 && fc < 0) )
{ /* Adjust c for it to have a sign*/
c = a; fc = fa; /* opposite to that of b */
}
}
}
--EDIT--
Thank you for everyone's suggestions, I've changed the format to ANSI format and changed EPSILON to DBL_EPSILON and also altered #include"math.h" to say #include - the updated function (is included below). However if I try to compile this time:
$gcc -Wall zeroin.c -o zeroin -lm
zeroin.c: In function 'zeroin':
zeroin.c:78:17: error: 'DBL_EPSILON' undeclared (first use in this function)
zeroin.c:78:17: note: each undeclared identifier is reported only once for each function it appears in
zeroin.c:116:7: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
Am is there maybe another library I need for DBL_EPSILON if it's saying that it's not defined?
Thanks, Ben.
#include <math.h>
double zeroin(double ax, double bx, double(*f)(double x), double tol) /* An estimate to the root */
{
double a,b,c; /* Abscissae, descr. see above */
double fa; /* f(a) */
double fb; /* f(b) */
double fc; /* f(c) */
a = ax; b = bx; fa = (*f)(a); fb = (*f)(b);
c = a; fc = fa;
for(;;) /* Main iteration loop */
{
double prev_step = b-a; /* Distance from the last but one*/
/* to the last approximation */
double tol_act; /* Actual tolerance */
double p; /* Interpolation step is calcu- */
double q; /* lated in the form p/q; divi- */
/* sion operations is delayed */
/* until the last moment */
double new_step; /* Step at this iteration */
if( fabs(fc) < fabs(fb) )
{ /* Swap data for b to be the */
a = b; b = c; c = a; /* best approximation */
fa=fb; fb=fc; fc=fa;
}
tol_act = 2*DBL_EPSILON*fabs(b) + tol/2;
new_step = (c-b)/2;
if( fabs(new_step) <= tol_act || fb == (double)0 )
{
return b; /* Acceptable approx. is found */
}
/* Decide if the interpolation can be tried */
if( fabs(prev_step) >= tol_act /* If prev_step was large enough*/
&& fabs(fa) > fabs(fb) ) /* and was in true direction, */
{ /* Interpolatiom may be tried */
register double t1,cb,t2;
cb = c-b;
if( a==c ) /* If we have only two distinct */
{ /* points linear interpolation */
t1 = fb/fa; /* can only be applied */
p = cb*t1;
q = 1.0 - t1;
}
else /* Quadric inverse interpolation*/
{
q = fa/fc; t1 = fb/fc; t2 = fb/fa;
p = t2 * ( cb*q*(q-t1) - (b-a)*(t1-1.0) );
q = (q-1.0) * (t1-1.0) * (t2-1.0);
}
if( p>(double)0 ) /* p was calculated with the op-*/
q = -q; /* posite sign; make p positive */
else /* and assign possible minus to */
p = -p; /* q */
if( p < (0.75*cb*q-fabs(tol_act*q)/2) /* If b+p/q falls in [b,c]*/
&& p < fabs(prev_step*q/2) ) /* and isn't too large */
new_step = p/q; /* it is accepted */
/* If p/q is too large then the */
/* bissection procedure can */
/* reduce [b,c] range to more */
/* extent */
}
if( fabs(new_step) < tol_act ) /* Adjust the step to be not less*/
if( new_step > (double)0 ) /* than tolerance */
new_step = tol_act;
else
new_step = -tol_act;
a = b; fa = fb; /* Save the previous approx. */
b += new_step; fb = (*f)(b); /* Do step to a new approxim. */
if( (fb > 0 && fc > 0) || (fb < 0 && fc < 0) )
{ /* Adjust c for it to have a sign*/
c = a; fc = fa; /* opposite to that of b */
}
}
}
999
This code uses the ancient pre-standard style of function signature, with the types of the parameters after the parameter list.
Change
double zeroin(ax,bx,f,tol) /* An estimate to the root */
double ax; /* Left border | of the range */
double bx; /* Right border| the root is seeked*/
double (*f)(double x); /* Function under investigation */
double tol; /* Acceptable tolerance */
{
to:
double zeroin(double ax, double bx, double (*f)(double), double tol)
{
There's surely a way to make gcc accept the old style, but unless you're worried about merge conflicts from upstream changes, you may as well just update it :-)
117
It looks like the filename has a capitalised extension, .C, which makes GCC think that it's C++ rather than C. The code is in an ancient dialect of C (known as "K&R style") which isn't compatible with C++.
Rename the file to zeroin.c, or specify the language on the command line with -x c.
Alternatively, if you need to use a compiler that doesn't understand K&R syntax, you could change the function header to use modern syntax:
double zeroin(double ax, double bx, double(*f)(double x), double tol)
{
// code here
}
The remaining problem is the use of EPSILON; in a modern C library, that's called DBL_EPSILON.
33
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