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, 13 Jun 2001
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An article on how to decode Base64 and Quoted-Printable text without using MFC.


There are already other articles here on The Code Project that shows how to decode Base64 and Quoted-Printable, but they all use MFC. I needed some code that didn't use MFC, so I wrote AMMimeUtils.

I wrote these classes because I was working with receiving and sending emails and Usenet messages. Almost all email messages and attachments are either Base64 or Quoted-Printable encoded. Attachments in Usenet messages are often UU encoded, I still need to write a class to handle this, but it might come in a later version.

When you get an email, the subject and other header fields might also be encoded, so this code also includes some code to decode these fields. Different mail programs encode the subject in different ways. The following text:

Just a small text (for demo), and some more text...

can look both like

=?iso-8859-1?Q?Just a small text =28for demo=29, and some more text...?=

or like

Just a small text =?iso-8859-1?Q?=28for demo=29?=, and some more text...

The first line is easy, because we can see that the entire string is encoded with Quoted-Printable (the ?Q? part means Quoted-Printable). In the second string, it's only a part of it that's encoded, so we have to get the first non-encoded part, decode the encoded part, and get the last non-encoded part, and add the 3 parts together to get the final subject.

I made a function char* MimeDecodeMailHeaderField(char *s); to handle this. If you have a string called s containing the subject you want to decode, simply call it like this:

s = MimeDecodeMailHeaderField(s);

Now s contains the decoded text.

I have 2 classes CBase64Utils and CQPUtils for general encoding and decoding of Base64 and Quoted-Printable. The interface looks like:

//class to handle all base64 stuff...
class CBase64Utils
  int ErrorCode;
  int GetLastError() {return ErrorCode;};
  //caller must free the result, bufsize holds the decoded length
  char* Decode(char *input, int *bufsize);
  //caller must free the result, bufsize is the length of the input buffer
  char* Encode(char *input, int bufsize);

//class to handle quoted-printable stuff
class CQPUtils
  char* ExpandBuffer(char *buffer, int UsedSize, 
             int *BufSize, bool SingleChar = true);
  int ErrorCode;
  int GetLastError() {return ErrorCode;};
  char* Decode(char *input); //caller must free the result
  char* Encode(char *input); //caller must free the result

The only difference is the Decode() and Encode() functions. Quoted-Printable is always text, therefore it only takes one parameter, the string containing encoded text, and returns a pointer to a new buffer containing the decoded text. Base64 might be an encoded binary file, so it puts the length of the returned buffer in the bufsize variable. Then it's possible to save the decoded buffer as a binary file.

Both classes have a function GetLastError(), if you decode something, and this variable is zero, everything is fine, if it's non-zero there was an error in the input, but you still get the (maybe) encoded/decoded result.

Right now, this code only has functions for what I needed when I wrote it. In the future, it I might add some better error handling.

If you want to know more about MIME and email messages, you can take a look at:

  • RFC 2045 - Multipurpose Internet Mail Extensions (MIME) Part One, Format of Internet Message Bodies
  • RFC 2046 - Multipurpose Internet Mail Extensions (MIME) Part Two, Format of Internet Message Bodies
  • RFC 2044 - Multipurpose Internet Mail Extensions (MIME) Part Three, Format of Internet Message Bodies


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

Anders Molin
Software Developer (Senior)
Denmark Denmark
Huh! Wink | ;-)

Comments and Discussions

BugMajor bug [modified] PinmemberPavel6729-Mar-12 5:06 
Generalunicode version Pinmembermengkim3-Apr-07 23:39 
GeneralNotice!!! Pinmembersongzd7-Dec-06 23:51 
GeneralBug in mail decoder Pinmembersuperagenteg23-Nov-06 0:24 
QuestionBUG when decode b64 HTML!? PinmemberKFC1234-Jul-06 22:45 
GeneralSmall, but nasty bugs :mad: Pinmemberscjurgen16-Sep-04 3:41 
General2 bugs found PinmemberDavid Connet28-Apr-04 14:45 
GeneralRe: 2 bugs found PinmemberNate Austin8-Mar-07 19:53 
GeneralQ-Printable decode improvement PinmemberIrek Zielinski13-Apr-04 9:53 
GeneralRe: Q-Printable decode improvement Pinsussthenickname19-Jan-05 10:55 
GeneralRe: Q-Printable decode improvement PinmemberIrek Zielinski19-Jan-05 11:21 
GeneralI think it is bug (base64 encode) PinmemberKiangGiap Lau8-Jan-04 17:52 
GeneralRe: I think it is bug (base64 encode) Pinmemberratzfatz19-Jan-04 0:27 
Generaldecoding string with many ISO PinmemberDevCrazy17-Jun-03 5:01 
GeneralBinary data PinmemberJuan Carlos Cobas6-Sep-02 0:10 
GeneralRe: Binary data PinmemberIrek Zielinski9-Apr-04 8:29 
GeneralGet Base64 Encoded Length PinmemberPaul Kissel22-Aug-02 9:25 
GeneralRe: Get Base64 Encoded Length PinmemberPaul Kissel22-Aug-02 9:49 

I see the line in your BASE64 encoder routine:
int alsize = ((bufsize * 4) / 3);
char *finalresult = (char*)calloc(alsize + ((alsize / MaxLineLength) * 2) + (10 * sizeof(char)), sizeof(char));
So you do the standard calc. of * 4 / 3. Then to add in 2 bytes for every line break. But what about this 10 extra bytes tack on at the end. Is this to account for any possible "=" padding characters???
Would this be correct to get the EXACT number of bytes required for the encoded buffer?:
int alsize = ((bufsize * 4) / 3); // Basic calc.
alsize = alsize + ((alsize / MaxLineLength) * 2) // Add CRLFs
while( bufsize % 4 != 0 ) // Add padding amount if needed.
I'd just to the encoding and get the length of the string returned but in my case I have to know the length beforehand.
--Paul K.Smile | :)
GeneralRe: Get Base64 Encoded Length PinmemberAnders Molin26-Aug-02 14:55 
Generalquoted-printable result truncated. PinmemberAnonymous2-Nov-01 14:06 
GeneralRe: quoted-printable result truncated. PinmemberAnonymous5-Nov-01 8:23 
GeneralRe: quoted-printable result truncated. PinmemberAnders Molin17-Nov-01 10:30 
GeneralBug in decode PinmemberAnonymous25-Oct-01 5:55 
QuestionIn the class CBase64,why the decode fun can't decode the jpg file whice had been encode?? PinmemberAnonymous17-Oct-01 18:02 
AnswerRe: In the class CBase64,why the decode fun can't decode the jpg file whice had been encode?? PinmemberAnders Molin19-Oct-01 11:09 
GeneralBug with resultlen of Decode PinmemberSTF17-Oct-01 6:25 
GeneralBug in Base64 encoding PinmemberCRahul26-Sep-01 6:01 
GeneralRe: Bug in Base64 encoding PinmemberAnders Molin26-Sep-01 8:45 
GeneralLinks to the RFC documents PinmemberUwe Keim14-Jun-01 23:49 

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