Convert CString to std::string and back

Question

Convert CString to std::string and back

Flaviu_ 1,031

I have the following string (got from an method):

ÉÛ3òBc ß™ î²íÈ. Á:˜"´ÑÌç°A×üí„2 91Nÿ

This is not quite ASCII, I am aware of that.

Now, If I convert it as CString:

CString s1(dec.c_str(), dec.size());

and then convert back:

std::string t1 = CStringA(s1);

I got:

TRACE("%d|%d|%d\n", dec.size(), s1.GetLength(), t1.size());

80|80|37

which is not the same. My question is: how can convert this strange std::string dec to CString and then back in order to get it back exactly the same ?

RLWA32 49,536 Reputation points

2022-04-25T13:11:25.053+00:00

What encoding is the "strange std::string" supposed to be?
Flaviu_ 1,031 Reputation points

2022-04-25T13:14:32.043+00:00

base64 decoded code (chars and digits)
RLWA32 49,536 Reputation points

2022-04-25T13:26:56.183+00:00

So its probably binary data. Yes?
Flaviu_ 1,031 Reputation points

2022-04-25T14:09:42.757+00:00

In fact, the original string it's base encoded 64, and the decoded string is that "strange std::string"

Ex. Original string is: "ME6mCK00cznsEHX/O2EMgw5MU7"
And the base 64 decoded string is ÉÛ3òBc ß™ î²íÈ. Á:˜"´ÑÌç°A×üí„2 91Nÿ
RLWA32 49,536 Reputation points

2022-04-25T14:15:23.03+00:00

Let me put it another way. The base 64 encoded string was created from binary data.

If that's the case I don't understand the purpose of trying to convert this binary data to a CString.
Michael Taylor 60,161 Reputation points

2022-04-25T14:28:56.187+00:00
That's not possible. If you base64 encoded "ME6m..." then you would have gotten back a string that has either 1 or 2 equals on the end, in most cases and a series of letters and digits for everything else. If you then base64 decode the string back you'll get the original "ME6m...", not what you posted. If you got something different back then base64 encoding would have corrupted your data.

$originalValue = "ME6mCK00cznsEHX/O2EMgw5MU7" $encodedValue = ConvertTo-Base64 $originalValue # encodedValue = TUU2bUNLMDBjem5zRUhYL08yRU1ndzVNVTc= $decodedValue = ConvertFrom-Base64 $encodedValue if ($originalValue -ne $decodedValue) { Write-Error "Data corrupted" }

This looks like a text encoding issue to me. I would wager that you encoded your string to base64 using a different character set (perhaps ASCII) than you are decoding it to (perhaps UTF-8). It would be useful if you posted the original code used to convert to Base64 and identify what your MFC code is being compiled against (MBCS, Unicode, etc).
Flaviu_ 1,031 Reputation points

2022-04-25T14:30:01.457+00:00

"The base 64 encoded string was created from binary data" No, the base 64 encoded string was created from chars, not from binary data.

This conversion is needed for storing in registry using CSettingsStore, which know *const char** (CString) - BOOL Write(LPCTSTR lpszValueName, LPCTSTR lpszVal)

Would be a better idea to use
BOOL Write(LPCTSTR lpszValueName, LPBYTE pData, UINT nBytes) from CSettingsStore ?
Viorel 122.6K Reputation points

2022-04-25T15:34:33.847+00:00
To store data as string, you can store the Base64 string.

For the shown data it is better to use CByteArray and std::vector.

To deal with strings, research this approach:

CStringA s1a = CStringA( s1, s1.GetLength( ) ); std::string t1( s1a, s1a.GetLength( ) );
Flaviu_ 1,031 Reputation points

2022-04-25T15:42:05.717+00:00
The code looks like that:

std::string dec = CMyObject::SomeMethod("w5MU7/nQClY98/xqQs+cLIDoua2xgX4Nyt9DeBk4="); // std::string dec = "ÉÛ3òBc ß™ î²íÈ. Á:˜"´ÑÌç°A×üí„2 91Nÿ "; CString s1(dec.c_str(), dec.size()); std::string t1 = CStringA(s1); TRACE("%d|%d|%d\n", dec.size(), s1.GetLength(), t1.size()); 80|80|37

So, dec contain ÉÛ3òBc ß™ î²íÈ. Á:˜"´ÑÌç°A×üí„2 91Nÿ, and from now one, the is no implication to base 64 encoding. However, if I put dec into CString, and then back to another std::string (t1), t1 has different size, which is not ok.
Flaviu_ 1,031 Reputation points

2022-04-25T16:10:50.087+00:00
Yes, if I write:

CStringA s1(dec.c_str(), dec.size()); std::string t1(s1, s1.GetLength());

then dec, s1, and t1 has the same correct size. In order to store this string into registry via CSettingsStore, I need to put it somehow into a CString, and then I have that issue ...
Michael Taylor 60,161 Reputation points

2022-04-25T16:53:37.437+00:00

You are posting 2 different sets of results to us. You originally said this:

In fact, the original string it's base encoded 64, and the decoded string is that "strange std::string"
Ex. Original string is: "ME6mCK00cznsEHX/O2EMgw5MU7"
And the base 64 decoded string is ÉÛ3òBc ß™ î²íÈ. Á:˜"´ÑÌç°A×üí„2 91Nÿ

Now your new code is saying the base64 string is this: w5MU7/nQClY98/xqQs+cLIDoua2xgX4Nyt9DeBk4=

That string is being reported as an invalid Base64 string in my code. Try using this site to identify what character encoding is actually valid so we can narrow down the issue.

Additionally you're taking the results and converting to a string in whatever encoding you're using. What encoding is that?

After you've gotten a valid string you are then converting to ANSI CStringA and converting that to a std:string which means your app better be compiling using ANSI otherwise you've just corrupted your string.
RLWA32 49,536 Reputation points

2022-04-25T21:02:28.867+00:00

Would be a better idea to use
BOOL Write(LPCTSTR lpszValueName, LPBYTE pData, UINT nBytes) from CSettingsStore ?

Well, based on your assertion that the data encapsulated in the "strange std::string" is valid then that is the path that makes the most sense to me. The data will be written to the registry as type REG_BINARY and no conversions are needed.
Flaviu_ 1,031 Reputation points

2022-04-26T08:16:54.217+00:00

I've stored std::string as CByteArray into registry without converting it and it is ok now.

Thank you all of you !

Your answer

RLWA32 49,536 Reputation points

2022-04-25T13:11:25.053+00:00

What encoding is the "strange std::string" supposed to be?
Flaviu_ 1,031 Reputation points

2022-04-25T13:14:32.043+00:00

base64 decoded code (chars and digits)
RLWA32 49,536 Reputation points

2022-04-25T13:26:56.183+00:00

So its probably binary data. Yes?
Flaviu_ 1,031 Reputation points

2022-04-25T14:09:42.757+00:00

In fact, the original string it's base encoded 64, and the decoded string is that "strange std::string"

Ex. Original string is: "ME6mCK00cznsEHX/O2EMgw5MU7"
And the base 64 decoded string is ÉÛ3òBc ß™ î²íÈ. Á:˜"´ÑÌç°A×üí„2 91Nÿ
RLWA32 49,536 Reputation points

2022-04-25T14:15:23.03+00:00

Let me put it another way. The base 64 encoded string was created from binary data.

If that's the case I don't understand the purpose of trying to convert this binary data to a CString.
Michael Taylor 60,161 Reputation points

2022-04-25T14:28:56.187+00:00

That's not possible. If you base64 encoded "ME6m..." then you would have gotten back a string that has either 1 or 2 equals on the end, in most cases and a series of letters and digits for everything else. If you then base64 decode the string back you'll get the original "ME6m...", not what you posted. If you got something different back then base64 encoding would have corrupted your data.

$originalValue = "ME6mCK00cznsEHX/O2EMgw5MU7" $encodedValue = ConvertTo-Base64 $originalValue # encodedValue = TUU2bUNLMDBjem5zRUhYL08yRU1ndzVNVTc= $decodedValue = ConvertFrom-Base64 $encodedValue if ($originalValue -ne $decodedValue) { Write-Error "Data corrupted" }

This looks like a text encoding issue to me. I would wager that you encoded your string to base64 using a different character set (perhaps ASCII) than you are decoding it to (perhaps UTF-8). It would be useful if you posted the original code used to convert to Base64 and identify what your MFC code is being compiled against (MBCS, Unicode, etc).
Flaviu_ 1,031 Reputation points

2022-04-25T14:30:01.457+00:00

"The base 64 encoded string was created from binary data" No, the base 64 encoded string was created from chars, not from binary data.

This conversion is needed for storing in registry using CSettingsStore, which know *const char** (CString) - BOOL Write(LPCTSTR lpszValueName, LPCTSTR lpszVal)

Would be a better idea to use
BOOL Write(LPCTSTR lpszValueName, LPBYTE pData, UINT nBytes) from CSettingsStore ?
Viorel 122.6K Reputation points

2022-04-25T15:34:33.847+00:00

To store data as string, you can store the Base64 string.

For the shown data it is better to use CByteArray and std::vector.

To deal with strings, research this approach:

CStringA s1a = CStringA( s1, s1.GetLength( ) ); std::string t1( s1a, s1a.GetLength( ) );
Flaviu_ 1,031 Reputation points

2022-04-25T15:42:05.717+00:00

The code looks like that:

std::string dec = CMyObject::SomeMethod("w5MU7/nQClY98/xqQs+cLIDoua2xgX4Nyt9DeBk4="); // std::string dec = "ÉÛ3òBc ß™ î²íÈ. Á:˜"´ÑÌç°A×üí„2 91Nÿ "; CString s1(dec.c_str(), dec.size()); std::string t1 = CStringA(s1); TRACE("%d|%d|%d\n", dec.size(), s1.GetLength(), t1.size()); 80|80|37

So, dec contain ÉÛ3òBc ß™ î²íÈ. Á:˜"´ÑÌç°A×üí„2 91Nÿ, and from now one, the is no implication to base 64 encoding. However, if I put dec into CString, and then back to another std::string (t1), t1 has different size, which is not ok.
Flaviu_ 1,031 Reputation points

2022-04-25T16:10:50.087+00:00

Yes, if I write:

CStringA s1(dec.c_str(), dec.size()); std::string t1(s1, s1.GetLength());

then dec, s1, and t1 has the same correct size. In order to store this string into registry via CSettingsStore, I need to put it somehow into a CString, and then I have that issue ...
Michael Taylor 60,161 Reputation points

2022-04-25T16:53:37.437+00:00

You are posting 2 different sets of results to us. You originally said this:

In fact, the original string it's base encoded 64, and the decoded string is that "strange std::string"
Ex. Original string is: "ME6mCK00cznsEHX/O2EMgw5MU7"
And the base 64 decoded string is ÉÛ3òBc ß™ î²íÈ. Á:˜"´ÑÌç°A×üí„2 91Nÿ

Now your new code is saying the base64 string is this: w5MU7/nQClY98/xqQs+cLIDoua2xgX4Nyt9DeBk4=

That string is being reported as an invalid Base64 string in my code. Try using this site to identify what character encoding is actually valid so we can narrow down the issue.

Additionally you're taking the results and converting to a string in whatever encoding you're using. What encoding is that?

After you've gotten a valid string you are then converting to ANSI CStringA and converting that to a std:string which means your app better be compiling using ANSI otherwise you've just corrupted your string.
RLWA32 49,536 Reputation points

2022-04-25T21:02:28.867+00:00

Would be a better idea to use
BOOL Write(LPCTSTR lpszValueName, LPBYTE pData, UINT nBytes) from CSettingsStore ?

Well, based on your assertion that the data encapsulated in the "strange std::string" is valid then that is the path that makes the most sense to me. The data will be written to the registry as type REG_BINARY and no conversions are needed.
Flaviu_ 1,031 Reputation points

2022-04-26T08:16:54.217+00:00

I've stored std::string as CByteArray into registry without converting it and it is ok now.

Thank you all of you !

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Convert CString to std::string and back

Your answer