C++ :: Cannot Cast From Void Pointer - Returns Always Error C2440
Apr 25, 2013
I having a problem which I'm not able to resovle. I try to dereference a void pointer but I always get a C2440 error. It says: 'static_cast':void* cannot be converted in wqueue<T>. I tried different cast ways but I always get the same error. As far as I found out I should get the error if I try to dereference without cast but in my case I cast before and still get that error.
In my refference book I have got a example with a part saying to access the a[4][0] element of the array (named a) with pointer this can be written:
*((int*)a+4)
I wonder if the cast is really required. The book says it is required so that the pointer arithmetic can be done properly. However I am not sure about it. When I work with pointers defined by myself I don't use casts similar to this one. Is there a difference between a self defined pointer and array name?
const void insertStuff(const void *key, const int value){ // I want to convert the void pointer into one // of three types of pointers(int, string, or double) switch(value){ case 0: int *intPtr = key;
[Code] .....
But this causes an error of: "crosses initialization of int*intPtr"
I cannot get the following to compile. The problem is the printf on the last line. I understand that printf requires a char (or pointer to char). I understand that I can convert between datatypes by putting the target data type in parenthises in front of the variable. But how do I cast the integer into a character and then get it's pointer to pass into printf?
Following is my code. I compile with gcc temp.c -o temp.
Note that I have tried many attempts at that last line and this is just the one that I really, really think should work (or is at least the closest to the correct answer).
This code shown below, using printf("%s", &(char)nextChar); returns
temp.c:26: error: lvalue required as unary '&' operand
If I try to use printf("%s", *(char)nextChar); I get the error
temp.c:26: error: invalid type argument of 'unary *' (have 'int')
This line printf("%s", (char)nextChar); returns the obvious
format '%s' expects type 'char *', but argument 2 has type 'int'
Code:
#include <stdio.h> int main() { printf("hello, world "); #if defined(SUNDIALS_EXTENDED_PRECISION)
I know that if I just use "return" by itself the warning goes away but fails to exit when the error occurs. I also believe this may not be the correct use of stderr. But I need the program to exit when an error has occurred.
The log file gives me: In function ‘memFileAlloc’ assignment makes pointer from integer without a cast..When compiling the drivers for the Matrox card in the DL580. The offending code is:
I create an instance of a base class (not derived class) and assign it to base class pointer. Then, I convert it to a pointer to a derived class and call methods on it.
why does it work, if there is a virtual table?
when will it fail?
// TestCastWin.cpp : Defines the entry point for the console application.//
Afterwards I'm using this as a check throughout my application:
if (dbCount > 0) { // do something }
When I execute this code I'm getting the following error: "Operator '>' cannot be applied to operands of type 'method group' and 'int'"
So I'm guessing it has something to do with the cast of the dbCount-object but I don't understand why as I already stated that the count-object to be an Int32.
I could understand void pointers I created the following program:
Code: #include <stdio.h> #include <string.h> int main(void) {
char word[] = "Zero"; int number = 0; void *ptr = NULL;
[Code] .....
The program works fine, however i really want to fully understand what is going on with the dereferencing of the void pointer, for example: With the following code:
Code: ptr = &number; *((int *)ptr) = 1;
Why can't you just do:
Code: ptr = &number; *(int *)ptr = 1;
And again with this code, (i'm guessing it's becuase its a pointer to a pointer?):
Why does the following code compile and execute without any error? I mean, the function compareid should get 2 arguments so why does the compiler not complaining, is it because of the type of arguments?
Code: #include <stdio.h> int compareid(void* info, int value); // ansi declaration int compareid(void* info, int value)
i need to return a struct pointer dynamically allocated inside a function call void function() which is done using 'out parameters' in following code
struct my_struct { int x; } void my_function( my_struct** result ) { my_struct* x = new my_struct{ 10 }; //... *result = x; }
Now i have a doubt, so if i want to print the return value from struct pointer, should i need to print it in the void function() or in the caller the function...
if possible i want avoid the '&' when i assign the variable address.(variant2 f=varname;//like you see i don't use the '&') for the moment i just need put the address to Variant pointer. but i receive several errors .
