I attempted to initialize char array with NULL like this syntax.
char str[5] = NULL;
But it returned error.. How can I initialize char array with NULL or 0 in C++?
Concretely, I want to print "Hello" in this example code.
#include <iostream>
int main()
{
char str[5] = NULL;
if(!str)
std::cout << "Hello" << std::endl;
return 0;
}
This code will return error because of incorrect initialization. Then, what initializing sentence should I replace sentence with?
An array can not be null. Null is state of a pointer, and an array is not a pointer.
In the expression !str, the array will decay to the address of the first element. The type of this decayed address is a pointer, but you cannot modify the decayed pointer. Since the array is never stored in the address 0 (except maybe in some special case on an embedded system where an array might actually be stored at that memory location), !str will never be true.
What you can do, is initialize all of the sub-objects of the array to zero. This can be achieved using the value-initialization syntax:
char str[5]{};
As I explained earlier, !str is still not meaningful, and is always false. One sensible thing that you might do is check whether the array contains an empty string. An empty string contains nothing except the terminator character (the array can have elements after the terminator, but those are not part of the string).
Simplest way to check whether a string is empty is to check whether the first character is the terminator (value-initialized character will be a terminator, so a value initialized character array does indeed contain the empty string):
if (!str[0]) // true if the string is empty
char, and everything to do with the difference between an array, and a pointer. A pointer stores a memory address. The address zero is the null pointer. An array is a sequence of objects in memory. It does not store an address.
//...
char str[5] = {'\0'};
if (str[0] != '\0')
//...
If you now put some characters into str it will print str up to the last '\0'. Every string literal ends with '\0', you must make sure your array ends with '\0' too, if not, data will be read beyond your array (until '\0' is encountered) and possibly beyond your application's memory space in which case your app will crash.
You should use std::string or QString however if you need a string.
const char *) ends in '\0'.You can't initialise a char array with NULL, arrays can never be NULL. You seem to be mixing up pointers and arrays. A pointer could be initialised with NULL.
You can initialise the chars of your array with 0, that would be
char str[5] = {0};
but I don't think that's what you're asking.
#include <stdio.h>
using namespace std;
int main() {
char str[5];
for(int i=0;i<5;i++){
str[i]=NULL;
}
printf("success");
return 0;
}
Hope this helps.
str[i]=NULL is wrong. NULL is a macro for a pointer literal. You shouldn't use it to initialize a character. Some hull pointer literals are character literals too (like 0), but others are not (nullptr), so this is not guaranteed to work.
char to 0. Surely not your intention, nor does it answer the question. Without a more precise definition of what you mean by "it works fine", this is not the answer.
char *str = NULL;Are you planning to modifystrlater or it remainsNULL?if(!str)you are checking if the pointer tostrisNULLnot if the content is0x0if(!str)- will never be true.stris an automatic variable with a determinate, non-null address. It does not have, and never will have, an expression value ofNULL. You need something that can holdNULL, and that is a pointer.char *str = NULL;, for example.