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POWhy does RegSetValueEx work even when I break the rule about accounting for NUL termination in the length?
 

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  1. POWhy does RegSetValueEx work even when I break the rule about accounting for NUL termination in the length?
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    <p>I've got a simple program that adds calc.exe to startup:</p> <pre><code>#include &lt;windows.h&gt; #include &lt;tchar.h&gt; int main(){ _tprintf(TEXT("Adding calc.exe to SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Run...\n")); HKEY hRegRunKey; LPCTSTR lpKeyName = TEXT("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Run"); LPCTSTR lpKeyValue = TEXT("Calculator"); LPCTSTR lpProgram = TEXT("C:\\WINDOWS\\system32\\calc.exe"); DWORD cchProgram = _tcslen(lpProgram); _tprintf(TEXT("Path: %s. \n"), lpProgram); _tprintf(TEXT("Length: %d. \n"), cchProgram); if(RegOpenKeyEx( HKEY_LOCAL_MACHINE, lpKeyName, 0, KEY_SET_VALUE, &amp;hRegRunKey) == ERROR_SUCCESS){ if(RegSetValueEx(hRegRunKey, lpKeyValue, 0, REG_SZ, (const BYTE *)lpProgram, cchProgram * sizeof(TCHAR)) != ERROR_SUCCESS){ _tprintf(TEXT("ERROR: Can't set key value.\n")); exit(1); }else{ _tprintf(TEXT("Key has been added sucessfully.\n")); } } Sleep(5000); RegCloseKey(hRegRunKey); } </code></pre> <p>For me the world of c/c++/WIN32API is still full of misteries... so I have few questions. </p> <p><strong>1. When I define string is it automatically null terminated?</strong></p> <pre><code>LPCTSTR lpProgram = TEXT("C:\\WINDOWS\\system32\\calc.exe"); </code></pre> <p>or should it be done:</p> <pre><code>LPCTSTR lpProgram = TEXT("C:\\WINDOWS\\system32\\calc.exe\0"); </code></pre> <p><strong>2. In my code is final argument to RegSetValueEx set to correct value?</strong></p> <p>From <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/ms724923%28v=vs.85%29.aspx" rel="nofollow">MSDN - RegSetValueEx function</a> page:</p> <blockquote> <p>cbData [in] The size of the information pointed to by the lpData parameter, in bytes. If the data is of type REG_SZ, REG_EXPAND_SZ, or REG_MULTI_SZ, cbData must include the size of the terminating null character or characters.</p> </blockquote> <p><strong>cchProgram</strong> is set to 28 characters <strong>without</strong> null termination. On my system(because of UNICODE I think?) <strong>cchProgram * sizeof(TCHAR)</strong> = 56. </p> <p>Shouldn't I set it to 58 to add null termination?</p> <hr> <p>When I run this program, as it is above, without any modifications and I'll check Calculator value in registry via <strong>Modify binary date</strong> I get:</p> <pre><code>43 00 3A 00 5C 00 57 00 C.:.\.W. 49 00 4E 00 44 00 4F 00 I.N.D.O. 57 00 53 00 5C 00 73 00 W.S.\.s. 79 00 73 00 74 00 65 00 y.s.t.e. 6D 00 33 00 32 00 5C 00 m.3.2.\. 63 00 61 00 6C 00 63 00 c.a.l.c. 2E 00 65 00 78 00 65 00 ..e.x.e. 00 00 .. </code></pre> <p>Its 58 bytes including null termination. I'am confuse:/</p> <p><strong>UPDATE</strong></p> <p>Accounting for a NULL character by adding 1 to string length when calculating <strong>cbData</strong> yields exactly same result as without adding it.</p> <blockquote> <p><strong>cchProgram * sizeof(TCHAR)</strong> produces same data entry as <strong>(cchProgram + 1) * sizeof(TCHAR)</strong></p> </blockquote> <p>Providing value smaller then a string length doesn't add NULL byte and copies given number of bytes.</p> <blockquote> <p><strong>27 * sizeof(TCHAR)</strong> as cbData produces:</p> </blockquote> <pre><code>43 00 3A 00 5C 00 57 00 C.:.\.W. 49 00 4E 00 44 00 4F 00 I.N.D.O. 57 00 53 00 5C 00 73 00 W.S.\.s. 79 00 73 00 74 00 65 00 y.s.t.e. 6D 00 33 00 32 00 5C 00 m.3.2.\. 63 00 61 00 6C 00 63 00 c.a.l.c. 2E 00 65 00 78 00 ..e.x. </code></pre> <p>I am on some old XP, service pack god knows what, I don't know how other version of windows would handle it. </p>
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    1. COApp of the information you provided in your subject should be tags, which means that you've posted no subject information here. Please [edit] your question and do so. Tag information belongs in the tags; the tagging system here is very good and doesn't need any help. Thanks.
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      1. USKen White
    2. CO@Ken White could you help me with that please? I cant find better title then this. I think that stack overflow has option for people to edit other people posts. Change it for more accurate title and I will definitely accept it.
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      1. USKocur4d
    3. CO@Kocur4d: Made your title into an on-topic summary, I hope that suits you.
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      1. USBen Voigt
 

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