C-Style unsigned char parsing and manipulation in C/C++ - segmentation fault

Question

Note that I'm using a C++ compiler ( hence, the cast on the calloc function calls) to do this, but the code is essentially C.

Basically, I have a typedef to an unsigned char known as viByte , which I'm using to create a string buffer to parse a file from binary (a TGA file, to be exact - but, that's irrelevant).

I'm writing basic functions for it right now; append, prepend, new, etc.

The problem is that, on the first iteration of the first loop in viByteBuf_Prepend , I get a segmentation fault. I need to know why, exactly, as this is something which could keep me up all night without some pointers (pun intended).

I also would like to know if my algorithms are correct in terms of how the buffer is pre-pending the viByte string. For example, I have a feeling that using memset too much might be a bad idea, and whether or not my printf format for the unsigned char is correct (I have a feeling it isn't, as nothing is getting output to my console).

Compiling on GCC, Linux.

Ze Code

#ifdef VI_BYTEBUF_DEBUG
void viByteBuf_TestPrepend( void )
{
    viByteBuf* buf = viByteBuf_New( 4 );

    buf->str = ( viByte* ) 0x1;

    printf(" Before viByteBuf_Prepend => %uc ", buf->str);

    viByteBuf_Prepend( buf, 3, ( viByte* ) 0x2 );

    printf(" After viByteBuf_Prepend => %uc ", buf->str);
}
#endif

viByteBuf* viByteBuf_New( unsigned int len )
{
    viByteBuf* buf = ( viByteBuf* ) calloc( sizeof( viByteBuf ), 1 );

    const int buflen = len + 1;

    buf->str = ( viByte* ) calloc( sizeof( viByte ), buflen );
    buf->len = buflen;

    buf->str[ buflen ] = '\0';

    return buf;
}

void viByteBuf_Prepend( viByteBuf* buf, unsigned int len, viByte* str )
{
    unsigned int pos, i;
    const unsigned int totallen = buf->len + len;
    viByteBuf* tmp = viByteBuf_New( totallen );
    viByte* strpos = buf->str;


    memset( tmp->str, 0, tmp->len );

    int index;

    for( i = 0; i < buf->len; ++i )
    {

       index = ( buf->len - i ) - 1;

       *strpos = buf->str[ 0 ];
       ++strpos;
    }

    memset( buf->str, 0, buf->len );

    printf( "%uc\n", buf->str );

    i = totallen;

    for ( pos = 0; pos < len; ++pos )
    {
        tmp->str[ pos ] = str[ pos ];
        tmp->str[ i ]   = buf->str[ i ];

        --i;
    }

    memset( buf->str, 0, buf->len );

    buf->len = tmp->len;

    memcpy( buf->str, tmp->str, tmp->len );

    viByteBuf_Free( tmp );

    //memset(  )
    //realloc( ( viByteBuf* ) buf, sizeof( viByteBuf ) * tmp->len );
}

Many thank yous.

Update

Sorry, I should have explicitly posted the code where the segmentation fault lies. It is right here:

for( i = 0; i < buf->len; ++i )
{

   index = ( buf->len - i ) - 1;

   *strpos = buf->str[ 0 ]; //<--segmentation fault.
   ++strpos;
}

Answer 1

On your code you have buf->str[ buflen ] = '\\0'; , but you only allocate space for buflen . I think you meant buf->str[ len ] = '\\0'; .