How can I resolve calloc() error in .cpp and .hpp files? - c++

Question

I try to run a .cpp with a .hpp file in Linux using this command: g++ -c main.cpp but I have this error about calloc():
error: there are no arguments to ‘calloc’ that depend on a template parameter, so a declaration of ‘calloc’ must be available [-fpermissive]
Tr=(T *)calloc(Rows*Colomns, sizeof(T));
In member function ‘T* MyMatrix::Adjoint()’:
MyMatrix.hpp:276:35: error: there are no arguments to ‘calloc’ that depend on a template parameter, so a declaration of ‘calloc’ must be available [-fpermissive]
Temp = (T*)calloc(N*N, sizeof(T));
I noticed that this code works in Microsoft Visual Studio:
#pragma once
#include <iostream>
#include <fstream>
template <typename T>
class MyMatrix {
private:
int Rows;
int Colomns;
T* A; //Matricea
T* Tr; //Transpusa acesteia
float* Inv; //Inversa
public:
MyMatrix(int L, int C)
{
Rows = L;
Colomns = C;
A = (T*)calloc(Rows * Colomns, sizeof(T));
if (A == NULL)
throw("Eroare la alocarea matricii! :(");
}
MyMatrix(T* S, int L, int C)
: MyMatrix(L, C)
{
for (int i = 0; i < Rows * Colomns; ++i)
A[i] = S[i];
}
~MyMatrix() { free(A); }
void Transposed()
{
Tr = (T*)calloc(Rows * Colomns, sizeof(T));
for (int i = 0; i < Colomns; ++i)
for (int j = 0; j < Rows; ++j)
Tr[j * Colomns + i] = A[i * Rows + j];
}
void Inverse()
{ //some code
T* Adj = Adjoint();
Inv = (float*)calloc(Rows * Rows, sizeof(float));
for (int i = 0; i < this->Rows * this->Rows; ++i)
Inv[i] = Adj[i] / (float)Det;
}
};
#endif // MYMATRIX_HPP_INCLUDED

Answer 1

a declaration of ‘calloc’ must be available
The solution is to declare calloc before using it. Since it is a standard function, it must be declared by including the standard header that is specified to declare it.
calloc is declared in the header <stdlib.h>. Note that the .h suffixed headers from the C standard library are deprecated in favour of using the c prefixed headers such as <cstdlib>. However, the c prefixed headers declare the functions in the std namespace which you have failed to use in this case.
So the complete solution is to include <cstdlib>, and use std::calloc.
However, you don't need to use calloc at all. Better solution is to use std::make_unique or std::vector.

Answer 2

As the error message suggests, the g++ compiler used here does not have an implementation wherein the second parameter is a template type i.e. the compiler recognizes the arguments when the second argument is of type int or float because these are the types the compiler knows about its 'calloc' implementation works with these types BUT it does not recognize when the second argument is of a templated type.
Visual Studio used here probably has an implementation which allows template types to be passed to 'calloc'.
Maybe you can try updating the g++ compiler to the latest and then it might support what you are trying to do here.
hope this helps!