这些指针中的哪一个需要free（）或delete（）

Question

I'm confused with freeing or deleting pointer. For what I have read I have to use free with malloc , calloc , realloc and delete with new

But what if :

char * hello = "helloworld"; //need to use free()?
char * pointerWmalloc= (char*) malloc(sizeof(char)); 
pointerWmalloc="This need free for sure";
//here need to use free() am I right ? 
char * dupOfHello = strdup(hello); //need to use  free()? 
char * thisWnew= new Char(); // this need delete for sure 
char * charReturnedByFunc= returnchar(); // need to use free() for charReturnedByFunc??

Answer 1

char * hello = "helloworld"; //need to use free()?

"helloworld" is a const char* and hello is now a dynamic reference to it. (You will trigger a runtime exception if you try to change any characters in the string, or free this memory)

char * pointerWmalloc = (char*)malloc(sizeof(char));

This allocated memory needs to be free 'd BEFORE reassignment to

pointerWmalloc = "This need free for sure";

which like hello now points to a const char * with the same restrictions.

char * dupOfHello = strdup(hello); //need to use  free()? 

this needs to be free 'd

char * thisWnew = new Char(); // this need delete for sure 

This does need delete . Also, Char is not a class unless you make it one, but I think you meant char()

char * charReturnedByFunc = returnchar(); // need to use free() for charReturnedByFunc??

This one is tricky, it completely depends on what returnchar() returns a pointer to. A const char* ? no. A char* owned by another object or function? Maybe. A char* allocated inside the function? Maybe. Unless you make it completely clear, you can't know if returnchar() returns a malloc 'd or new 'd char* .

All this and more is why it's recommended to avoid raw pointers in favor of std::unique_ptr and std::shared_ptr , avoid malloc in favor of new , and avoid char* in favor of std::string .

Answer 2

I'll answer with comments in the code below:

char * hello = "helloworld"; // Do not free/delete pointer
                             // `hello` points to read-only memory
char * pointerWmalloc= (char*) malloc(sizeof(char)); // use free(pointerWmalloc) here
pointerWmalloc="This need free for sure"; // now you created a memory leak since pointerWmalloc now points to read-only memory. So do not free/delete

char * dupOfHello = strdup(hello); // use free(dupOfHello) here (as documented) 
char * thisWnew= new char(); // use delete thisWnew here
char * charReturnedByFunc= returnchar(); // need to read the documentation.
                // could be free, delete, none of the two or something else