Cannot convert from 'const wchar_t *' to '_TCHAR *'

Question

_TCHAR* strGroupName = NULL;
const _TCHAR* strTempName = NULL;

//Assign some value to strTempName

strGroupName = _tcschr(strTempName, 92) //C2440

I get an error at the above line while compiling this code in VS2008. In VC6 it compiles fine.

Error C2440: '=' : cannot convert from 'const wchar_t *' to '_TCHAR *'

What seems to be the problem and how do I fix it?

Averment

Answer 1

Try casting it as

strGroupName = (_TCHAR*)_tcschr(strTempName, 92);

Seems to me that VS2008 got a little more strict on type casts, and won't automatically do them in some cases.

Mesarch

Answer 2

strGroupName = const_cast<_TCHAR*>( _tcschr(strTempName, 92));

This is because the variant of the function you're using has a const _TCHAR* as input and returns a const _TCHAR*.

Another variant would be to have strTempName declared as _TCHAR*, and not as const _TCHAR*. In this case, the variant function having a _TCHAR* parameter and returning a _TCHAR* value is used.

Freeload

Is Jack's answer fine? It got rid of the compilation error but I want to know the difference between his and yours. – Averment

This version is better: it allows you to be specific about what the cast is for, i.e. it's not casting from some unrelated type, it's just removing the const. – Bombast

@Bobby Using const_cast operation will allow you to easy find the const casting in the code by performing a simple search. I don't recomment const casting unless is really necessary. The second alternative (make strTempName as non-const) is my preferred, because it implies no further constness changing. Btw, is any reason why you declared strTempName as const? – Solanum

Answer 3

_tcschr is returning a const pointer. Hence the return value should be const _TCHAR* strGroupName = NULL; If it is not possible to change strGroupName to a const pointer then declare both the pointers as non-const pointers.

Nonsuit

This is fine but I cannot change strGroupName to const because it will affect the rest of the code which does not expect a const variable. Functions for example. – Averment

Then make strTempName & strGroupName both non-const. – Nonsuit

+1 including the comment that both can be non-const (perhaps add it to the answer?) – Bombast

Answer 4

strGroupName should also be a pointer to const.

const _TCHAR* strGroupName = _tcschr(strTempName, 92);

No need to declare it until the call to initialise it.

Bombast

Answer 5

I got the same error when moving from C++14->20, was able to fix it by setting /Zc:StrictStrings- under CommandLine in my build properties.

Adanadana