Stupid C problem [solved]
Author
Consider this:
if(!knowledge_list.name)return 0;//doesn't work
vs
if(!knowledge_list.name[0])return 0;//works
Any idea why the first doesn't work?
[Edited by - Raduprv on June 9, 2005 10:47:05 PM]
I could be wrong, but, I think the first checks if the pointer value of name is == 0, which since its created on the stack means its probably not true... the second version checks if the first element is 0 which would be true if you zerod out the array.
The first you're trying to convert a char array into a boolean. That isn't possible. In the second, however, you're trying to convert a number (a char, to be precise) into a boolean. This is possible (0 = false, anything else = true).
Author
Hmm
I also tried: if(!&knowledge_list.name)return 0;
Still doesn't work.
Shouldn't that point at the first char in the string?
I also tried: if(!&knowledge_list.name)return 0;
Still doesn't work.
Shouldn't that point at the first char in the string?
if(!knowledge_list.name)return 0;//doesn't work
Will evaluate the address of the first element.
Since the address will be something other then 0(true), NOT'ed will be false.
To verify this do: if(!*(knowledge_list.name))return 0;//should work
if(!knowledge_list.name[0])return 0;//works
Will evaluate the content of the first element.
Here the content will allways be zero, NOT'ed will be true.
Will evaluate the address of the first element.
Since the address will be something other then 0(true), NOT'ed will be false.
To verify this do: if(!*(knowledge_list.name))return 0;//should work
if(!knowledge_list.name[0])return 0;//works
Will evaluate the content of the first element.
Here the content will allways be zero, NOT'ed will be true.
Author
Quote:Original post by xor
if(!knowledge_list.name)return 0;//doesn't work
Will evaluate the address of the first element.
Since the address will be something other then 0(true), NOT'ed will be false.
To verify this do: if(!*(knowledge_list.name))return 0;//doesn't work
if(!knowledge_list.name[0])return 0;//works
Will evaluate the content of the first element.
Here the content will allways be zero, NOT'ed will be true.
You are right!
God, I really shouldn't program when I am tired. Wasted half an hour with this stupid thing.
Quote:Original post by Raduprv
Hmm
I also tried: if(!&knowledge_list.name)return 0;
Still doesn't work.
Shouldn't that point at the first char in the string?
maybe you could do if(!knowledge_list.name+1) ?
EDIT: actually, you might have to dereference that.
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