Using a vector of pointers to loop other vectors

Question

I have created a class including among other things vectors. I would like to loop these vectors and have therefore in my class constructor created a vector of pointers to these vectors. It compiles OK but it doesn't run properly. Debugging seems to show that there is a problem with the vector.size() although it appears on the cout line. I have shorten the class and the code to make it easier to read but I still get the error.

This is the class definition:

#ifndef DEFINITION_CLASSES
#define DEFINITION_CLASSES

#include <string>
#include <vector>
#include <stdarg.h>

using namespace std;

class objLoc {
public:
    vector<string> branches;
    void setBranches(int amount, ...);
};
void objLoc::setBranches(int amount, ...) {
    char *value;
    va_list points;

    branches.clear();
    va_start(points, amount);
    for (int i = 0; i < amount; ++i) {
        value = va_arg(points, char *);
        branches.push_back(string(value));
    }
    va_end(points);
}

class Spline3d {
public:
    vector<double> x, y, z;
    objLoc location;
    void setx(int amount, ...);
};
void Spline3d::setx(int amount, ...) {
    double value;
    va_list points;

    x.clear();
    va_start(points, amount);
    for (int i = 0; i < amount; ++i) {
        value = va_arg(points, double);
        x.push_back(value);
    }
    va_end(points);
}

class SuspensionGeneralProperties {
public:
    Spline3d left_x_vs_z, left_y_vs_z, right_x_vs_z, right_y_vs_z;
};

class Suspension {
public:
    Suspension();
    SuspensionGeneralProperties suspProp;
    vector<Spline3d *> variable_spline3d;
};
Suspension::Suspension() {
    Spline3d * temp_spline3d[] = { &suspProp.left_x_vs_z, &suspProp.left_y_vs_z,
            &suspProp.right_x_vs_z, &suspProp.right_y_vs_z };
    variable_spline3d.assign(temp_spline3d, temp_spline3d + 5);
}

#endif

And here is the source file:

#include <iostream>
#include <string>
#include <vector>
#include <stdarg.h>
#include "class_def.h"

using namespace std;

void loop(Suspension* susp) {
    Spline3d* spline;

    for (size_t i = 0; i < susp->variable_spline3d.size(); i++) {
        spline = susp->variable_spline3d[i];
        cout << "Branch: " << spline->location.branches[0] << endl; //This is where the error seems to be
    }
}

int main() {
    int i;
    Suspension suspFront;

    suspFront.suspProp.left_x_vs_z.setx(11, -100.0, -80.0, -60.0, -40.0, -20.0,
            0.0, 20.0, 40.0, 60.0, 80.0, 100.0);
    suspFront.suspProp.left_x_vs_z.location.setBranches(3, "Subsystem",
            "SuspensionGeneralProperties", "Spline3d");
    suspFront.suspProp.left_y_vs_z.setx(11, -100.0, -80.0, -60.0, -40.0, -20.0,
            0.0, 20.0, 40.0, 60.0, 80.0, 100.0);
    suspFront.suspProp.left_y_vs_z.location.setBranches(3, "Subsystem",
            "SuspensionGeneralProperties", "Spline3d");
    suspFront.suspProp.right_x_vs_z.setx(11, -100.0, -80.0, -60.0, -40.0, -20.0,
            0.0, 20.0, 40.0, 60.0, 80.0, 100.0);
    suspFront.suspProp.right_x_vs_z.location.setBranches(3, "Subsystem",
            "SuspensionGeneralProperties", "Spline3d");
    suspFront.suspProp.right_y_vs_z.setx(11, -100.0, -80.0, -60.0, -40.0, -20.0,
            0.0, 20.0, 40.0, 60.0, 80.0, 100.0);
    suspFront.suspProp.right_y_vs_z.location.setBranches(3, "Subsystem",
            "SuspensionGeneralProperties", "Spline3d");

    loop(&suspFront);

    cin >> i;
    return i;
}

I would be very grateful for any leads that can help me solve this.

Prefer vector<unique_ptr<Spline3d>> and let the vector do its job. — Ed Swangren
– Ed Swangren, Commented Dec 12, 2012 at 21:26
As the variadic logic in stdarg.h is done via macros, have you looked at the source with the macros expanded to see if there's any problems that jump out at you? — Maurice Reeves
– Maurice Reeves, Commented Dec 12, 2012 at 21:34

Remy Lebeau · Accepted Answer · 2012-12-12 22:13:44Z

2

variable_spline3d.assign(temp_spline3d, temp_spline3d + 5);

You are telling assign() to copy five Spline3D* pointers but there are only four pointers in your array, so the 5th pointer is garbage.

edited Dec 12, 2012 at 22:13

answered Dec 12, 2012 at 21:26

Remy Lebeau

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2 Comments

Yakk - Adam Nevraumont Over a year ago

@Bill, reconsider. [&foo, &foo+1) contains how many elements?

Yakk - Adam Nevraumont Over a year ago

@Bill and thus there are 5 elements in [temp_spline3d, temp_spline3d + 5), and Remy is right in that there is a problem.

dchellaram · Accepted Answer · 2012-12-12 21:18:46Z

1

You are not checking to see what the size of spline->location.branches is. It's likely that there is an empty branches vector and you are attempting to access a nonexistent element.

answered Dec 12, 2012 at 21:18

dchellaram

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