Another Linker Error?

Question

Tinee 0 Light Poster

15 Years Ago

Hi,

I'm trying to find the resultant of a given data using fstream. I made the program and everything and I believe its all correct however, when I try to run it, I'm getting a linker error saying "undefined reference to Resultant(const double...)" which I can't figure out how to fix it. Can you please help me spot the problem?

Thank you in advance.

This is the program:

#include <iostream>
#include <fstream>
#include <iomanip>
#include <cstring>
#include <cmath>

using namespace std;

void Resultant(const double[], const double[], const double[], const double[], const int,
                double&, double&, double&);

const double PI=acos(-1.0);
int main()
{
    const int size = 200 ;
    int moves = 0;
    double Magnitude[size], X_axis[size], Y_axis[size], Z_axis[size];
    double X_Resultant=0, Y_Resultant=0, Z_Resultant=0;
    string choice, answer;
    
    cout << "This program will calculate the Resultant Forces from a "
         << "selected data sheet.";
         
        do 
        {      
    cout << "\n\nPlease type in the data sheet you want to be calculated?"
         << "\nEnter Force1 or Force2 : " ;
    cin >> choice;
                
    if (choice == "Force1" || "force1")
    {
                        ifstream Data("Forces1.DAT");
 
                                  if (Data.fail())
                                     cout <<"\nFail To Open\nCheck File" << endl;
 
           for ( int i=0; !Data.eof();i++)
               {
                  Data >> Magnitude[i] >> X_axis[i] >> Y_axis[i] >> Z_axis[i];
                   moves++;
                                   }     
                     Data.close();   break;
     }
    
    else if (choice == "Force2" || "force1")
    {
                        ifstream Data("Forces2.DAT");
 
                                  if (Data.fail())
                                     cout <<"\nFail To Open!\nCheck File" << endl;
 
                  for ( int i=0; !Data.eof();i++)
                  {
        Data >> Magnitude[i] >> X_axis[i] >> Y_axis[i] >> Z_axis[i];
        moves++;
                                   }     
        Data.close(); break;
     }
     
            else {
                     cout << "\nERROR! Invalid Input! \nWould you like to"
                          << " try again? Enter y or n : " ;
                      cin >> answer;
                          }
}
     while (answer == "y" || answer == "Y");                   
     
     Resultant(Magnitude, X_axis, Y_axis, Z_axis, moves, X_Resultant, Y_Resultant, Z_Resultant);
     
     cout << setw(6) << X_Resultant << setw(6) << Y_Resultant << setw(6) << Z_Resultant;
     
system("pause");
return 0;
}

void Resultant(const double M[], const double X[], const double Y[], double Z[],
const int moves, double& Rx, double& Ry, double& Rz)
 {
      double Fx[moves], Fy[moves],Fz[moves];
        for (int i=0; i<3; i++) // using 3 to test the program
        {
        Fx[i]= M[i]*cos(X[i]*180/PI);
        Fy[i]= M[i]*cos(Y[i]*180/PI);
        Fz[i]= M[i]*cos(Z[i]*180/PI);
        }

        for (int i=0; i<3; i++)
        {
            Rx += Fx[i];
            Ry += Fy[i];
            Rz += Fz[i];
        }
        
 }

c++

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Latest Post 15 Years Ago Latest Post by Tinee

Dani AI

Generated 9 Months Ago

The linker error was caused by the function-prototype/definition mismatch that and spotted: the declared signature in main does not exactly match the defined signature, so the compiler emits a reference to one mangled name while the linker can't find a definition for it. Make the declaration and the definition identical (same parameter types, same const qualifiers and linkage) and recompile.

A short checklist for "undefined reference" problems:

Ensure the prototype and definition exactly match (cv-qualifiers like const on parameter types matter).
Confirm the definition is compiled and linked into the final binary (all .o/.cpp files included).
Watch for different linkage (e.g., extern "C" vs C++), namespaces, or member vs free functions.
Turn on warnings (-Wall -Wextra for gcc/clang, enable MSVC warnings) and, if needed, inspect object-file symbols with nm/c++filt to see what symbol the linker is missing.

Other issues in the posted code worth fixing now:

Cosine expects radians. Convert degrees to radians with angle * PI / 180.0 (the original 180/PI is the inverse).
Variable-length arrays like Fx[moves] are non-standard in C++; prefer std::vector<double> or reserve and push values.
Avoid for(...; !Data.eof(); ...) for file reads. Use a read-while loop such as while (Data >> a >> b >> c >> d) to avoid partial/invalid reads or buffer overruns.

A clearer design: store each force in a small struct and pass a std::vector of those to a single function that returns the resultant. Example pattern (illustrative):

struct Force { double magnitude, degX, degY, degZ; };

Force compute_resultant(const std::vector<Force>& forces) {
    Force R{0,0,0,0}; // use R.degX/R.degY/R.degZ as Rx,Ry,Rz
    for (const auto &f : forces) {
        double rx = f.magnitude * cos(f.degX * PI / 180.0);
        // accumulate rx, ry, rz into R.degX/R.degY/R.degZ
    }
    return R;
}

The signature fix noted by / and the string-comparison fix pointed out by are the immediate fixes; the design suggestions above improve safety and maintainability going forward.

All 8 Replies

vijayan121 1,152 Posting Virtuoso

15 Years Ago

Declaration

void Resultant(const double[], const double[], const double[], [B]const[/B] double[], const int, double&, double&, double&);

does not match the definition

void Resultant(const double M[], const double X[], const double Y[], [B]/* ??? */[/B] double Z[], const int moves, double& Rx, double& Ry, double& Rz)
{
   // ...

Not a great idea, writing a function with eight(!) parameters.

Edited 15 Years Ago by vijayan121 because: n/a

fibbo 0 Light Poster

15 Years Ago

check the implementation of your Resultant function. You forgot the const on Z[].

vij beat me to it!

Edited 15 Years Ago by fibbo because: n/a

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Tinee 0 Light Poster · Answer 1 · 2011-04-02T02:01:58+00:00

wow you guys are right. silly me. haha. what is the best way to pass 8 variables to a function? just curious.

Tinee 0 Light Poster · Answer 2 · 2011-04-02T02:02:15+00:00

Tinee 0 Light Poster

15 Years Ago

thank you for finding my mistake.

fibbo 0 Light Poster · Answer 3 · 2011-04-02T04:40:44+00:00

Well on the top of my head I have 2 "solutions" for passing less variables.

1 defining the variables global
or passing a vector of doubles and a vector of arrays of doubles.

Take this with a big grain of salt and wait for a competent coder with his opinion. I just try to get some opinions as well (because on another project I work on I pass alot of variables as well).

Tinee 0 Light Poster · Answer 4 · 2011-04-03T12:56:06+00:00

i see but this project is recording numbers from a file thats why im passing a lot of variables. hehe. your right though it's unsafe.

i have a problem with my program :( . i don't know how or what happen but suddenly it doesn't go to "else" statement saying "try again" if i type in random words, it just goes to the first "if". my "else if" and "if" statements records the right file when i type in the correct word phrase. any idea why this is happening?

this is the do while loop:

do{      
                        
    cout << "\n\nPlease type in the data sheet you want to be calculated?"
         << "\nEnter Forces1 or Forces2 : " ;
    cin >> file;
    
      
    if (file == "Forces1" || "forces1")
    {
                        ifstream Data("Forces1.DAT");
 
                                  if (Data.fail())
                                     cout <<"\nFail To Open! Check File If Created" << endl; 
                 
           for ( int i=0; !Data.eof();i++)
               {
                  Data >> Magnitude[i] >> X_axis[i] >> Y_axis[i] >> Z_axis[i];
                   moves++;
                                   }     
                     Data.close(); 
     }
    
    else if (file == "Forces2" || "forces1")
    {
                        ifstream Data("Forces2.DAT");
 
                                  if (Data.fail())
                                     cout <<"\nFail To Open! Check File If Created" << endl; 
 
                  for ( int i=0; !Data.eof();i++)
                  {
        Data >> Magnitude[i] >> X_axis[i] >> Y_axis[i] >> Z_axis[i];
        moves++;
                                   }     
        Data.close(); 
     }
     
            else {
                     cout << "\nERROR! Invalid Input! \nWould you like to"
                          << " try again? Enter y or n : " ;
                      cin >> answer;
                          }
}
     while (answer == "y" || answer == "Y");

jonsca 1,059 Quantitative Phrenologist Team Colleague Featured Poster · Answer 5 · 2011-04-03T14:46:39+00:00

if (file == "Forces1" || "forces1")

must be

if(file == "Forces1" || file == "forces1")

otherwise, in the first instance it's evaluating "forces1" as true since it is not null, so your statement's always true.

Same thing for the else if condition, too.

Tinee 0 Light Poster · Answer 6 · 2011-04-06T13:38:08+00:00

thank you for pointing that out. i got it to work because of you guys.

Another Linker Error?

Dani AI

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