I'm trying to compile my main.cpp, but I keep getting this error for two hours now. The issue here is to pass a function as a parameter but I think I'm doing something wrong. The compiler says it cannot find the function, but I included "newt_rhap(params)" in the "functions.h" already.
I did the returnType (*functionName)(paramType), but I may have skipped something here. The code of my friends doesn't need the recently mentioned syntax. What is wrong here?
I tried using both -std=c++11 and -std=c++98. The gcc/g++ compiler came from my Xcode command line tools.
g++ (or gcc) -std=c++98(or 11) main.cpp -o main.out
There was no difference in error.
**error: no matching function for call to 'newt_rhap'**
./functions.h:5:8: note: candidate function not viable: no known conversion from 'double' to
'double (*)(double)' for 1st argument
double newt_rhap(double deriv(double), double eq(double), double guess);
Here is the code.
// main.cpp
#include <cmath>
#include <cstdlib>
#include <iostream>
#include "functions.h"
using namespace std;
// function declarations
// =============
// void test(double d);
// =============
int main(int argc, char const *argv[])
{
//
// stuff here excluded for brevity
//
// =============
do
{
// line with error
guess = newt_rhap(eq1(guess),d1(guess),guess);
// more brevity
} while(nSig <= min_nSig);
// =============
cout << "Root found: " << guess << endl;
return 0;
}
Then functions.h and functions.cpp, respectively
// functions.h
#ifndef FUNCTIONS_H_INCLUDED
#define FUNCTIONS_H_INCLUDED
// ===========
double newt_rhap(double deriv(double), double eq(double), double guess);
// ===========
// ===========
double eq1(double x);
double d1(double x);
// ===========
#endif
// functions.cpp
#include <cmath>
#include "functions.h"
using namespace std;
// ===========
double newt_rhap(double (*eq)(double ) , double (*deriv)(double ), double guess)
{
return guess - (eq(guess)/deriv(guess));
}
// ===========
// ===========
double eq1(double x)
{
return exp(-x) - x;
}
double d1(double x)
{
return -exp(-x) - 1;
}
Instead of:
guess = newt_rhap(eq1(guess),d1(guess),guess);
try:
guess = newt_rhap(eq1, d1, guess);
The function takes two functions and a guess as arguments. By passing eq1(guess)
you are passing a double, not a function (the evaluated result of eq1
with an argument of guess
)
The signature of your function prototype in functions.h
does not match the signature of the function you implement in functions.cpp
.
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