Need some HELP with a function return

Question

Need some HELP with a function return

TIM 61

Please do not judge; I am out of my element in C++., but trying to learn. Again, please do not judge - I am trying to use a function that decrypts an AES 256 bit message with CAPICOM. When I run my program in the VC++ (VS 2008) debugger, I can clearly see the decrypted string in _bstr_t variable:( plainText). When the value is passed back to the calling program, the content is missing. Here is the function call in my program, and the entire CAPICOM Decrypt function. I have a C background, and proficient in VB. Trying to wrap my addled brain around the necessary * chars below satisfied the compiler. ANY and ALL assistance will be so very appreciated - I've hit the wall.

Tim

*sDataCID = *Decrypt(sDataCID, sKey);

char *Decrypt(char *pszStr, char *pszKey)
{
int size;
char *buf;
//char plainText;
_bstr_t plainText;

IEncryptedDataPtr encryptor;

size = strlen(pszStr);

buf = new char[size + 1];
buf[size] = 0;

encryptor.CreateInstance("CAPICOM.EncryptedData");

encryptor->SetSecret(_bstr_t(pszKey), CAPICOM_SECRET_PASSWORD);

encryptor->Decrypt(_bstr_t(pszStr));
plainText = encryptor->GetContent();


return plainText;

}

Barry Schwarz 5,756 Reputation points

2022-03-03T18:31:24.03+00:00

plainText is local to you function. It comes into existence when you enter the function. At that time, its constructor is called. It goes out of existence when you exit the function. At that time, its destructor is called. Depending on the types of objects in the class, their destructors may also be called recursively. This may result in the loss of the data that you see before the function returns.

Additionally, randomly adding an * to a function declaration to satisfy a diagnostic is not a recipe for success.

Second addition, you never use buf. Allocating memory for it to point to is a waste. More importantly, you never release the allocation. This causes a memory leak. Depending on how often you call this function and the amount of data you pass it, this may be an issue for your system.

Third addition, the new operator does not initialize the memory it allocates. After setting the last allocated byte to zero, you have no idea what is in the first size-1 bytes. They are all indeterminate. The terminal zero serves no purpose, especially since there may be random zeros in the first bytes.
Viorel 127K Reputation points

2022-03-03T18:33:52.377+00:00

Try changing the function to '_bstr_t Decrypt(char *pszStr, char *pszKey)'. Maybe other changes are not needed.
TIM 61 Reputation points

2022-03-03T19:08:06.063+00:00

Thank you ALL for the ideas. I belabored more than a day deciding to post my question; ignorance is no excuse for pestering professionals - and I didn't want to waste others time. I tried the suggestions provided, and should have included how the " char sDataCID[255]; " was defined in MAIN, not globally. BarrySchwarz-8780 is absolutely correct that slinging * (content of) at the compiler is not a plan for sucess. If you would postulate a theory as to how to define sDataCID so that it can receive a _bstr_t value, I will be honored. Again, THANK YOU ALL for the guidance.

Tim
YujianYao-MSFT 4,296 Reputation points Microsoft External Staff

2022-03-04T09:40:31.717+00:00

Hi @TIM ,

Do you have to use the API? Regarding AES 256, more people choose to use C#, you could refer to this issue.
WayneAKing 4,936 Reputation points

2022-03-05T22:57:43.647+00:00
the new operator does not initialize the memory it allocates.
After setting the last allocated byte to zero, you have no
idea what is in the first size-1 bytes. They are all
indeterminate.

As a further observation on this, to have the new operator
default-initialize the allocation you should add parentheses
to the end of the new statement. This will cause all elements
of the allocation to be set to the default value for the
data type (if known).

int size = strlen("example"); char *buf; buf = new char[size + 1]; // uninitialized elements buf[size] = 0; char *buf2; buf2 = new char[size + 1](); // initializes elements to binary zero

Wayne
TIM 61 Reputation points

2022-03-05T23:27:32.483+00:00

To all who offered ideas, THANK YOU. This turned out to be an exercise in futility: VC++ 2008 Express Edition does not contain ANY conversion Macro's or tools, so every method I tried failed. It took a while to figure it out. I am embarrassed, and was fairly sure I could figure it out. All is well, and everything works as it is supposed to.
Tim

Answer accepted by question author

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Barry Schwarz 5,756 Reputation points

2022-03-03T18:31:24.03+00:00

plainText is local to you function. It comes into existence when you enter the function. At that time, its constructor is called. It goes out of existence when you exit the function. At that time, its destructor is called. Depending on the types of objects in the class, their destructors may also be called recursively. This may result in the loss of the data that you see before the function returns.

Additionally, randomly adding an * to a function declaration to satisfy a diagnostic is not a recipe for success.

Second addition, you never use buf. Allocating memory for it to point to is a waste. More importantly, you never release the allocation. This causes a memory leak. Depending on how often you call this function and the amount of data you pass it, this may be an issue for your system.

Third addition, the new operator does not initialize the memory it allocates. After setting the last allocated byte to zero, you have no idea what is in the first size-1 bytes. They are all indeterminate. The terminal zero serves no purpose, especially since there may be random zeros in the first bytes.
Viorel 127K Reputation points

2022-03-03T18:33:52.377+00:00

Try changing the function to '_bstr_t Decrypt(char *pszStr, char *pszKey)'. Maybe other changes are not needed.
TIM 61 Reputation points

2022-03-03T19:08:06.063+00:00

Thank you ALL for the ideas. I belabored more than a day deciding to post my question; ignorance is no excuse for pestering professionals - and I didn't want to waste others time. I tried the suggestions provided, and should have included how the " char sDataCID[255]; " was defined in MAIN, not globally. BarrySchwarz-8780 is absolutely correct that slinging * (content of) at the compiler is not a plan for sucess. If you would postulate a theory as to how to define sDataCID so that it can receive a _bstr_t value, I will be honored. Again, THANK YOU ALL for the guidance.

Tim
YujianYao-MSFT 4,296 Reputation points Microsoft External Staff

2022-03-04T09:40:31.717+00:00

Hi @TIM ,

Do you have to use the API? Regarding AES 256, more people choose to use C#, you could refer to this issue.
WayneAKing 4,936 Reputation points

2022-03-05T22:57:43.647+00:00

the new operator does not initialize the memory it allocates.
After setting the last allocated byte to zero, you have no
idea what is in the first size-1 bytes. They are all
indeterminate.

As a further observation on this, to have the new operator
default-initialize the allocation you should add parentheses
to the end of the new statement. This will cause all elements
of the allocation to be set to the default value for the
data type (if known).

int size = strlen("example"); char *buf; buf = new char[size + 1]; // uninitialized elements buf[size] = 0; char *buf2; buf2 = new char[size + 1](); // initializes elements to binary zero

Wayne
TIM 61 Reputation points

2022-03-05T23:27:32.483+00:00

To all who offered ideas, THANK YOU. This turned out to be an exercise in futility: VC++ 2008 Express Edition does not contain ANY conversion Macro's or tools, so every method I tried failed. It took a while to figure it out. I am embarrassed, and was fairly sure I could figure it out. All is well, and everything works as it is supposed to.
Tim

Answer 1

Castorix31 91,876

You can see Example: Convert from _bstr_t

or you can declare :

LPWSTR Decrypt(char* pszStr, char* pszKey)

then

  LPWSTR pString = Decrypt(sDataCID, sKey);

TIM 61 Reputation points

2022-03-03T22:24:57.17+00:00

Castorix31,
Thank you for the reply. I tried your suggestion; with my best understanding - it did not solve the issue. Learning while doing is always problematic. Is there any more data I might provide to make this clearer? I've been experimenting most of the afternoon, but making no progress, and I have been scouring the MS Docs for answers.

Tim
RLWA32 52,571 Reputation points

2022-03-04T10:54:15.56+00:00

Posting the code for your unsuccessful attempts and indicating the specific problems encountered would enable the community to further assist you.

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Need some HELP with a function return

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