How to convert a string to Unsigned char in visual c++

Question

How to convert a string to Unsigned char in c++...

I have,

unsigned char m_Test[8];

i want to assign a string "Hello world" to the m_Test.

how to do it ?

Answer 1

you can use strcpy function But have in mind that m_Test is only 8 size and there will be an overflow. Strcpy won't check that and you will get an exception

char * strcpy ( char * destination, const char * source );

Answer 2

You can use c_str() function of std::string to get the char* out of string. This method basically returns a pointer to c-style string. After this you can use the normal string copying functions such as strcpy or strncpy to copy the value in to test.

Answer 3

You can use strcpy:

unsigned char m_Test[8];
strcpy((char*)m_Test, "Hello world");

Note that "Hello world" is too long for 8 bytes, so you will probably get a segfault.

Answer 4

You can use a string copy function like strcpy or even beeter strncpy, which has also some size checks:

strncpy ((char*) m_Test,"Hello World",8);

Answer 5

strncpy(m_Test, "Hello world", sizeof(m_Test));

Here's Wikipedia on strncpy:

Answer 6

Firstly, the array has to be at least big enough to hold the string:

 unsigned char m_Test[20];

then you use strcpy. You need to cast the first parameter to avoid a warning:

 strcpy( (char*) m_Test, "Hello World" );

Or if you want to be a C++ purist:

 strcpy( static_cast <char*>( m_Test ), "Hello World" );

If you want to initialise the string rather than assign it, you could also say:

 unsigned char m_Test[20] = "Hello World";

Answer 7

For all practical purposes, the strcpy answers are correct, with the note that 8 isn't big enough for your string.

If you want to be really pedantic, you might need something like this:

#include <algorithm>

int main() {
    const char greeting[] = "Hello world";
    unsigned char m_Test[sizeof(greeting)];
    std::copy(greeting, greeting + sizeof(greeting), m_Test);
}

The reason is that std::copy will convert the characters in the original string to unsigned char. strcpy will result in the characters in the original string being reinterpreted as unsigned char. You don't say which one you want.

The standard permits there to be a difference between the two, although it's very rare: you'd need char to be signed, in an implementation with a 1s' complement or sign-magnitude representation. You can pretty much ignore the possibility, but IMO it's worth knowing about, because it explains the funny warnings that good compilers give you when you mix up pointers to char and unsigned char.