# Gavin Andresen
# 2010-07-24 01:44:02
# https://bitcointalk.org/index.php?topic=555.msg5424#msg5424

They key bits of code are: @p{brk}

Code:
fileout @p{lt}@p{lt} FLATDATA(pchMessageStart) @p{lt}@p{lt} nSize; @p{brk}
... @p{brk}
fileout @p{lt}@p{lt} *this;
pchMessageStart are the four magic bytes, and those are written with FLATDATA. @p{par}

The CBlock itself is written by @p{lt}@p{lt} *this, and that's done by the IMPLEMENT_SERIALIZE in main.h: @p{brk}

Code:
    IMPLEMENT_SERIALIZE @p{brk}
    ( @p{brk}
        READWRITE(this-@s{gt}nVersion); @p{brk}
        nVersion = this-@s{gt}nVersion; @p{brk}
        READWRITE(hashPrevBlock); @p{brk}
        READWRITE(hashMerkleRoot); @p{brk}
        READWRITE(nTime); @p{brk}
        READWRITE(nBits); @p{brk}
        READWRITE(nNonce); @p{par}

        // ConnectBlock depends on vtx being last so it can calculate offset                                              @p{brk}
        if (!(nType & (SER_GETHASH|SER_BLOCKHEADERONLY))) @p{brk}
            READWRITE(vtx); @p{brk}
        else if (fRead) @p{brk}
            const_cast@p{lt}CBlock*@s{gt}(this)-@s{gt}vtx.clear(); @p{brk}
    ) @p{brk}

 @p{brk}
The READWRITE macros Do The Right Thing, reading in or writing out the members in a machine-independent way. @p{par}

See @s{(link)} for simplified Python code that can dump out transactions and blocks. @p{par}