string conversion

Question

I have some doubts about the string conversions in C++.

1. To convert const WCHAR* to LPWSTR can I use the below code? LPWSTR dest;
   const WCHAR* source =L"Hello";
   dest = 0;
   wcsncpy_s(dest, MAX_PATH, source , wcsnlen_s(source , MAX_PATH));
   2. I am trying to assign a const WCHAR* to WCHAR*. I am aware that we can remove the constness using const_cast . Is there any other way to make the assignment?

Answer 1

You may find this helpful -- how-to-convert-between-various-string-types

If you simply want a copy of a string you can use strdup-wcsdup-mbsdup

Answer 2

LPWSTR dest;
const WCHAR* source =L"Hello";
dest = 0;
wcsncpy_s(dest, MAX_PATH, source , wcsnlen_s(source , MAX_PATH));

That code will cause an address exception. You have set dest to 0 (NULL)
and then tried to copy data to that address.

• Wayne

Answer 3

wcsncpy_s(dest, MAX_PATH, source, wcsnlen_s(source, MAX_PATH));

You are misusing the arguments that define the max size of dest and source.
That defeats the whole purpose of those parameters. They act as security
safeguards against buffer overruns by providing the max number of characters
that the respective buffers may use. i.e. - The actual sizes.

The second argument should specify the max number of characters that may be
copied to dest. At run time an error will occur if an attempt is made to write
beyond the end of the dest buffer. This prevents security vulnerabilities
caused by overrunning the buffer when writing to it.

The fourth argument should specify the max number of characters that may be
read from source. That prevents reading past the end of that buffer if the
contents do not contain a terminating nul character. At run time an error
will occur if an attempt is made to read beyond the end of the source buffer,
as defined by the size you have provided.

You are lying to the compiler by supplying false information about the
respective sizes of the buffers. Therefore at run time buffer overruns
will go undetected as you have told the compiler that the buffers are
bigger than they actually are.

MAX_PATH is not a relevant or accurate value to use for these arguments.

• Wayne