Bart <bc@[EMAIL PROTECTED]
> writes:
> On May 6, 11:45 am, "Kevin" <yushuma...@[EMAIL PROTECTED]
> wrote:
>> Source:
>> #include <stdio.h>
>> #include <ctype.h>
>> void main()
>> {
>> char a[]="this is the beautiful world!";
>> char b[20];
>> strcpy(b,a);
>> printf("char array b size is(%d),The content of b
is:%s\n",sizeof(b),b);
>> if(strcmp(a,b)==0)
>> printf("a equal to b!\n");
>>
>> }
>>
>> Now , question as follows:
>>
>> 1. Why "b" size unequal "a" size , but "b" can output "a" content?
>> 2. Why "if(strcmp(a,b)==0)" is true?
>
> a and b are different types:
Yes.
> a is a pointer to a string
No, a is an array of type char[29] (the length of the literal used to
initialize it plus 1 for the trailing '\0').
> b /is/ a string.
No, b is an array of type char[20]. An array can *contain* a string.
A "string" in C is a a data format, not a data type.
> But a can obviously point to a string identical to what's in b.
The object named ``a'' can't point to anything, since it's an array,
not a pointer. However, the expression ``a'', in most but not all
contexts, has the value of a pointer to (the address of) the first
element of the object named ``a''.
> The size of a will be 4 or whatever, the size of b will be 20
> (although it should be more in this case otherwise your "this is..."
> string will overflow it).
No, sizeof a == 20.
> strcmp() compares two pointers to strings; but b is automatically
> converted to such a pointer, thanks to the way C handles arrays.
I think the other errors in the program have already been pointed out,
but ...
Drop the ``#include <ctype.h>''; it's not needed.
Add ``#include <string.h>''; it *is* needed.
Change ``void main()'' to ``int main(void)''.
Change ``char b[20];'' to, for example, ``char b[30];''.
In the printf call, change ``sizeof(b)'' to ``(int)sizeof b'';
the "%d" format requires an int, not a size_t.
Before the closing brace, add ``return 0;''.
Enable warnings in your compiler, and buy some whitespace (it's really
cheap).
--
Keith Thompson (The_Other_Keith) <kst-u@[EMAIL PROTECTED]
>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
|
