Re: C++ - how to convert string to uppercase/lowercase
On Dec 17, 10:46 pm, Noah Roberts <n...@nowhere.com> wrote:
sean_in_rale...@yahoo.com wrote:
You have to create my_toupper (or use a cast) due to a
C++ wart.
What wart?
To begin with, the fact (inherited from C) that you can't call
toupper with a char without encurring undefined behavior.
#include <cctype>
#include <algorithm>
#include <string>
#include <iostream>
int main()
{
std::string x = "hello world";
transform(x.begin(), x.end(), x.begin(), toupper);
std::cout << x << std::endl;
}
Works fine in VS and G++.
Like his original code, it has undefined behavior. Unlike his
original code, there's also a very good chance that it won't
compile. There are two problems: the use of toupper is
ambiguous; this is easily resolved by including <ctype.h>
instead of <cctype>, and specifying ::toupper. The second
problem is more subtle: ::toupper takes an int as argument, not
a char, and it has a pre-condition that the value is in the
range 0...UCHAR_MAX (or EOF). If plain char is signed (as is
all too often the case), calling it with a plain char results in
undefined behavior. (There are other problems with this
solution, e.g. ::toupper uses mutable global state, which may
cause problems in a multithreaded environment. But they don't
apply here.)
And of course, there's the more general problem that transform
can't handle case transformations, because there's not a one to
one mapping of lower case to upper case. But that issue affects
any code which attempts to use any of the toupper functions in
the standard library.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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