Problems with wchar and registry entry

Question

So I want to add a string to registry, since the registry strings are to written NULL terminated my string contains a null char in various places.

This is what my string looks like.

char names[550] = "1DFA-3327-*\01DFA-3527-*\001DFA-E527-*\00951-1500-

I convert this to whcar_t string like so.

wchar_t names_w[1000];
size_t charsConverted = 0;
mbstowcs_s(&charsConverted, names_w, names, SIZE);
RegSetValueEx(*pKeyHandle, valueName, 0, REG_MULTI_SZ, (LPBYTE)names_w, size);

The registry entry should be

1DFA-3327-*
1DFA-3527-*
1DFA-E527-*
0951-1500-*
0951-0004-*
0951-160D-*

But this is the registry entry now,

1DFA-3327-*
<a box here>DFA-3527-*
<a box here>DFA-E527-*
951-1500-*
951-0004-*
951-160D-*

So it eats up the 0 in 0951 also eats up the 1 in 1DFA

What I have tried:

1> I tried changing the string to

char names[550] = "1DFA-3327-*\0\01DFA-3527-*\0\001DFA-E527-*\0\00951-1500-

                              ^ ^ Two nulls

2> I tried different conversion.

for(int i; i < SIZE; i++)
   names_w[i] = (wchar_t)names[i];

@Stargateur This is related to Windows registry. One type of registry entry is a multi string which consists of multiple null terminated strings. Thus the '\0' as separator and a double '\0' as terminator. — Werner Henze, Nov 06 '17 at 12:06

Werner Henze · Accepted Answer · 2017-11-06T12:15:43.910

The problem is in your string literal.

char names[550] = "1DFA-3327-*\01DFA-3527-*\001DFA-E527-*\00951-1500-...\0";
                               ^^           ^^^           ^^

You can provide ASCII characters in octal notation (\ooo) or in hexadecimal notation (\x hh). In your case you provide octal notation and this eats up the next up to three characters. You should change your string to

char names[550] = "1DFA-3327-*\0001DFA-3527-*\0001DFA-E527-*\0000951-1500-...\0";

or

char names[550] = "1DFA-3327-*\0"  // put null byte at end of GUID
                  "1DFA-3527-*" "\0" // add null byte as extra literal
                  "1DFA-E527-*" "\0"
                  "0951-1500-...\0";

which also makes it easier to identify the GUIDs in the string.

If you want to use hexadecimal notation then take care that these might eat more than two bytes, so you also need to work with the literal concatenation. (See How to properly add hex escapes into a string-literal?)

char names[550] = "1DFA-3327-*\x00"  // put null byte at end of GUID
                  "1DFA-3527-*" "\x00" // add null byte as extra literal
                  "1DFA-E527-*" "\x00"
                  "0951-1500-...\x00";

BTW, is there any reason not to directly store a wide char string?

wchar_t names[550] = L"1DFA-3327-*\x001DFA-3527-*\x001DFA-E527-*\x000951-1500-...\0";

Thanks this solved it. Although I need to split the string as `"1DFA-3327-*" "\x0" "01DFA-3527"` — qwn, Nov 06 '17 at 12:09
Note: Hexadecimal escapes are not necessarily limited to 2 characters, as highlighted in [this question](https://stackoverflow.com/q/45612822/694733). — user694733, Nov 06 '17 at 12:10
@qwn That's a good idea. It helps keeping an overview over all the GUIDs and makes it easier to separate the GUIDs from each other and from the null bytes. — Werner Henze, Nov 06 '17 at 12:10

Problems with wchar and registry entry

1 Answers1