C++ style cast from unsigned char * to const char *

Jack_48461 0
Viewed 126421

I have:

unsigned char *foo();
std::string str;
str.append(static_cast<const char*>(foo()));

The error: invalid static_cast from type ‘unsigned char*’ to type ‘const char*’

What's the correct way to cast here in C++ style?

constants casting c++
7 Answers

char * and const unsigned char * are considered unrelated types. So you want to use reinterpret_cast.

But if you were going from const unsigned char* to a non const type you'd need to use const_cast first. reinterpret_cast cannot cast away a const or volatile qualification.

Brian_R_Bondy_31530

Try reinterpret_cast

unsigned char *foo();
std::string str;
str.append(reinterpret_cast<const char*>(foo()));
JaredPar_232830

reinterpret_cast

user_116350

You would need to use a reinterpret_cast<> as the two types you are casting between are unrelated to each other.

Timo_Geusch_290680

Too many comments to make to different answers, so I'll leave another answer here.

You can and should use reinterpret_cast<>, in your case

str.append(reinterpret_cast<const char*>(foo()));

because, while these two are different types, the 2014 standard, chapter 3.9.1 Fundamental types [basic.fundamental] says there is a relationship between them:

Plain char, signed char and unsigned char are three distinct types, collectively called narrow character types. A char, a signed char, and an unsigned char occupy the same amount of storage and have the same alignment requirements (3.11); that is, they have the same object representation.

(selection is mine)

Here's an available link: https://en.cppreference.com/w/cpp/language/types#Character_types

Using wchar_t for Unicode/multibyte strings is outdated: Should I use wchar_t when using UTF-8?

user_2077910
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