CODEWITHSUNDEEP
c++templatesstatic-methods
mmm
mmm

Reputation: 1297

Templated static member functions in C++

I've written a simple test program to try to learn how to use template static member functions in C++. The code compiles, but doesn't work right (prints out some garbage). I guess I'm using the right syntax. I've read this or this and some other stuff but still don't know what I'm doing wrong. The code below:

#include <iostream>
using namespace std;

class Util {
public:
    Util();
    virtual ~Util();

    template <typename T> static void printTab(T tab[]);
};

template <typename T>
void Util::printTab(T tab[]) {
    for (unsigned int i=0; i<sizeof(tab)/sizeof(tab[0]); i++) {
        cout << tab[0] << " ";
    }
    cout << endl;
}

int main() {

    float tabFloat[5] {1, 2, 3, 4, 5};
    unsigned char tabChar[3] {1, 2, 3};

    Util::printTab(tabFloat);
    Util::printTab(tabChar);

    return 0;
}

Any hints appreciated.

Upvotes: 4

Views: 275

Answers (4)

mechanicker
mechanicker

Reputation: 986

How about trying, you need to send the size of the array when calling a function:

#include <iostream>
using namespace std;

class Util {
public:
    Util();
    virtual ~Util();

    template <typename T> static void printTab(T tab[], size_t sz);
};

template <typename T>
void Util::printTab(T tab[], size_t sz) {
    for (unsigned int i=0; i<sz; i++) {
        cout << tab[i] << " ";
    }
    cout << endl;
}

int main() {

    float tabFloat[5] {1, 2, 3, 4, 5};
    unsigned char tabChar[3] {1, 2, 3};

    Util::printTab(tabFloat, sizeof(tabFloat)/sizeof(float));
    Util::printTab(tabChar, sizeof(tabChar)/sizeof(char));

    return 0;
}

Upvotes: 1

BЈовић
BЈовић

Reputation: 64293

You need to pass the size as another template argument : 

#include <iostream>
using namespace std;

class Util {
public:
    Util();
    virtual ~Util();

    template <typename T,int N> static void printTab(T (&tab)[N])
    {
        for (int i=0; i<N; i++) {
            cout << tab[i] << " ";
        }
        cout << endl;
    }
};

int main() {

    float tabFloat[5] {1, 2, 3, 4, 5};
    unsigned char tabChar[3] {1, 2, 3};

    Util::printTab(tabFloat);
    Util::printTab(tabChar);
}

Upvotes: 5

Doug Moscrop
Doug Moscrop

Reputation: 4544

I'd pass the number of elements of T as a function argument or use a STD container such as a Vector.

Your for loop is just printing the first element tab[0] not tab[i]

Your initialization of tabFloat and tabChar are missing =

float tabFloat[5] {1, 2, 3, 4, 5}; 
unsigned char tabChar[3] {1, 2, 3};

(also I'd use 65, 66, 67 instead of 1,2,3 for console readability in your testing)

float tabFloat[5] = {1, 2, 3, 4, 5}; 
unsigned char tabChar[3] = { 65, 66, 67};

Upvotes: -1

Mat
Mat

Reputation: 206909

sizeof(tab) is the size of a T*, it will not return the size of the whole array. You need to pass that in yourself as another argument to the function. See here for an explanation and another potential workaround: When a function has a specific-size array parameter, why is it replaced with a pointer?

Note that the second printTab will not output readable characters. If you want to see something printed out, try with:

 unsigned char tabChar[3] {'1', '2', '3'};

Upvotes: 2

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