Check for null character C++

Question

I'm trying to test if the value stored in a particular memory address is NULL, I have this and in debug it's showing the char value in that address as '\0'. Yet it's always skipping over this IF statement.

Is this the right syntax to use? I have ensured that the address is set to null.

if (test->address + length == NULL)
{
    ..code..
}

NULL is a null pointer, '\0' is a null character.

Barmar
– Barmar

2015-04-14 13:39:09 +00:00
Commented Apr 14, 2015 at 13:39 — Barmar
– Barmar, Commented Apr 14, 2015 at 13:39
What is the type of address?

Aaron McDaid
– Aaron McDaid

2015-04-14 13:42:08 +00:00
Commented Apr 14, 2015 at 13:42 — Aaron McDaid
– Aaron McDaid, Commented Apr 14, 2015 at 13:42
What about using a std::string if you are in C++ ?

Aracthor
– Aracthor

2015-04-14 13:44:03 +00:00
Commented Apr 14, 2015 at 13:44 — Aracthor
– Aracthor, Commented Apr 14, 2015 at 13:44

Mike Seymour · Accepted Answer · 2015-04-14 13:37:37Z

6

Assuming address is a char* pointer (or a char[] array), you need to dereference it to access the char values. That's

*(test->address + length)

or equivalently

test->address[length]

answered Apr 14, 2015 at 13:37

Mike Seymour

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Comments

Vlad from Moscow · Accepted Answer · 2015-04-14 13:43:28Z

4

If I have understood you correctly then the valid statement will look like

if ( *( test->address + length ) == '\0' )
{
    ..code..
}

Or

if ( test->address[length] == '\0' )
{
    ..code..
}

provided that type of object test->address either defined as a character array or a pointer of type char *

answered Apr 14, 2015 at 13:43

Vlad from Moscow

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Comments

Mateusz Grzejek · Accepted Answer · 2015-04-14 13:40:04Z

1

Of course it skips this if. That's because pointers arithmetic rules.

test->address is a pointer
test->address + length is test->address + sizeof(T) * length, where T is the type of address.

Change:

if (test->address + length == NULL)
{
    ..code..
}

to

if (test->address[length] == 0)
{
    ..code..
}

answered Apr 14, 2015 at 13:40

Mateusz Grzejek

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