如何在二进制文件中写入指针？ （C）

Question

I am not very used to work with a file, but when is necessary to write strings or normal variables, I don't find any problem to put them inside a binary file. However, I have tried several times to save the content of a pointer to pointer (actually, an array of strings) inside a b-file and all the time or my compiler showed an error or just crashed. Does someone have an idea of how to make it work?

A simplified version of the code is down there:

int main(){
  int n;
  scanf("%d", &n);

  char **campo2 = (char**)malloc(n*sizeof(char*));
  campo2[i] = (char*)malloc(20*sizeof(char));

  for(int i = 0; i< n; i++){
      campo2[i] = foo();
  }

  FILE *binaryFile = fopen("file.bin", "wb");

  if (binaryFile =! NULL){
    for(int i = 0;i<n;i++){
        fwrite(campo2[i], 20*sizeof(char),1,binaryFile);
    }
  }

  return 0;
 }

Answer 1

You probably want something like

char * foo(int i)
{
    char *s= malloc(20);
    fprintf(s,"%018d\r\n",i);
    return s;
}
int main()
{
    int n;
    scanf("%d", &n);

    char **campo2 = (char**)malloc(n*sizeof(char*));

    for(int i = 0; i< n; i++){
      campo2[i] = foo(i);
    }

    FILE *binaryFile = fopen("file.bin", "wb");

    if (binaryFile =! NULL){
        for(int i = 0;i<n;i++){
            fwrite(campo2[i], 20,1,binaryFile);
        }
        fclose(binaryFile);
    }
    return 0;
}