为什么我从“不兼容类型'void *'”错误中“分配'int *'？

Question

I'm learning c on codeacademy and I get an assigning to 'int *' from incompatible type 'void *' error. My file is a .c file, which includes stdlib.h. I don't understand the error, it seems that the corrections uses the same lines of code.

I'm trying to create an array using malloc.

I tried to find the answer on other topics. It seems that malloc is not the best way to do it but i would like to find a way to make it work.

I'm on a mac, I use emacs to code et gcc to compile.

Here's a part of my code :

int main(int argc, char *argv[])
{
  char mot_secret[] = "PISCINE";
  int nombre_lettres = strlen(mot_secret);
  int *pnombre_lettres = &nombre_lettres;
  int *decouverte = NULL;
  int compteur = 10;

  decouverte = malloc(nombre_lettres * sizeof(int));
  if (decouverte == NULL)
    {
      exit(0);
    }

And here's the solution : ( I tried to translate some of the variables)

int main(int argc, char* argv[])
{
    char lettre = 0;
    char secretword[100] = {0};
    int *lettreTrouvee = NULL; 
    long coupsRestants = 10; // Compteur de coups restants (0 = mort)
    long i = 0;
    long wordSize = 0;

    wordSize = strlen(secretWord);

    lettreTrouvee = malloc(tailleMot * sizeof(int)); // creates a dynamic array of the size of the original)
    if (lettreTrouvee == NULL)
        exit(0);

The error is :

TP.C:17:16: error: assigning to 'int *' from incompatible type 'void *'
  decouverte = malloc(nombre_lettres * sizeof(int));

Thank you very much for your help and I'm sorry if I make any mistakes in English.

Answer 1

It appears that your file's name is TP.C .

In the unix tradition, C source files are named *.c (lowercase c), and C++ source files are named *.C (capital C). The alternative *.cpp is used on Windows because of its case-ignorant filesystem, but gcc on MacOS is sufficiently unix-like that it is treating your *.C file as C++.

Answer 2

Given this error message:

 TP.C:17:16: error: assigning to 'int *' from incompatible type 'void *' decouverte = malloc(nombre_lettres * sizeof(int)); 

it appears your file is named TP.C . The upper-case .C file extension causes GCC to compile the file as C++ :

 file.cc file.cp file.cxx file.cpp file.CPP file.c++ file.C 

C++ source code that must be preprocessed. Note that in '.cxx', the last two > must both be literally 'x'. Likewise, '.C' refers to a literal capital C.

You need to use lower-case. Rename your file so that it ends with a .c - lower-case c .

Answer 3

The type returned from malloc is always void*, which can be cast to the desired type of data.

You will need to do: (int*) malloc(nombre_lettres * sizeof(int));

source: cplusplus