Replicate unpack of perl in c++ [closed] - c++

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I have a binary string with ASCII like this
^#^#^#^A^#^#^#^#^#^#^#^#^#^#^#^#^#^#^#^A^#^#^#^#^#^#^#^#^#^#^#^#^#^#^#^A^#^#^#^#^#^#^#^#^#^#^#^#^#^#^#^A^#^#^#^#^#^#^#^#^#^#^#^#^#^#^#^A^#^#^O ^#^#^#^#^#^BÜ-^#^#^#^A^#^#^O ^#^#^#^#^#^BÜ-^#^#^#^A^#^#^#^#^#^#^#^#^EÜ?^#^#^#^A^#^#^#^#^#^#^#^#^EÜ?^#^#^#^A^#^#.à^#^#^#^#^#^Häð^#^#^#^A^#^#.à^#^#^#^#^#^Häð^#^#^#^A^#^#><80>^#^#^#^#^#^KÖ<80>^#^#^#^A^#^#><80>^
Perl code:
#!/usr/bin/env perl
use warnings;
use strict;
use Data::Dumper;
open(INDEX, $ARGV[0]);
binmode(INDEX);
my $buff;
my $ret = read(INDEX, $buff, 4);
my $fragment = unpack 'N', $buff;
$ret = read(INDEX, $buff, 4);
my $timestamp = unpack 'N', $buff;
$ret = read(INDEX, $buff, 8);
my $offset = unpack 'N', $buff;
print "timestamp = $timestamp fragment # $fragment offset = $offset\n";
Output:
timestamp = 0 fragment # 1 offset = 0
timestamp = 0 fragment # 1 offset = 0
timestamp = 0 fragment # 1 offset = 0
timestamp = 0 fragment # 1 offset = 0
timestamp = 4000 fragment # 1 offset = 187437
timestamp = 4000 fragment # 1 offset = 187437
timestamp = 8000 fragment # 1 offset = 384063
timestamp = 8000 fragment # 1 offset = 384063
timestamp = 12000 fragment # 1 offset = 582896
timestamp = 12000 fragment # 1 offset = 582896
I want to replicate the above work done by unpack in C++
How to do it?
What I was trying:
#include <iostream>
#include <stdlib.h>
using namespace std;
int main ()
{
int k;
char buf1[5];
char buf2[5];
char buf3[9];
int i;
char *str;
//Assume str contains the entire binary data
for(int i=0;str[i];)
{
while(k<32)
{
buf1[k]=str[i];
++k;++i;
}
k=0;
while(k<32)
{
buf2[k]=str[i];
++k;
}
k=0;
while(k<64)
{
buf3[k]=str[i];
++k;++i;
}
k=0;
uint32_t a1,b1,a2,b2;
uint64_t a3,b3;
a1=atoi(buf1);
b1=ntohl(a1);
a2=atoi(buf2);
b2=ntohl(a2);
a3=atoi(buf1);
b3=ntohl(a3);
print "timestamp ="<< b2 << "fragment #"<<b1<<" offset ="<<b3<<"\n";
}
return 0;
}

Answer 1

Here you go:
#include <stdint.h>
#include <iostream>
#include <fstream>
using namespace std;
int main( int argc, char *argv[] )
{
if (argc < 2)
{
cerr << "Input filename required" << endl;
return 1;
}
ifstream f( argv[1], ios::binary );
if (!f.good())
{
cerr << "Cannot open input file '" << argv[1] << "'" << endl;
return 1;
}
while (!f.eof())
{
uint8_t buf[8];
f.read( reinterpret_cast< char * >( buf ), 4 );
uint32_t fragment = ( ( buf[0] * 256U + buf[1] ) * 256U + buf[2] ) * 256U + buf[3];
f.read( reinterpret_cast< char * >( buf ), 4 );
uint32_t timestamp = ( ( buf[0] * 256U + buf[1] ) * 256U + buf[2] ) * 256U + buf[3];
f.read( reinterpret_cast< char * >( buf ), 8 );
uint64_t offset = ( ( ( ( ( ( buf[0] * 256LL + buf[1] ) * 256LL + buf[2] ) * 256LL + buf[3] )
* 256LL + buf[4] ) * 256LL + buf[5] ) * 256LL + buf[6] ) * 256LL + buf[7];
if (f.good())
{
cout << "timestamp = " << timestamp;
cout << " fragment = " << fragment;
cout << " offset = " << offset << endl;
}
}
return 0;
}

Answer 2

Read 4 bytes, then use
uint32_t n;
n = buf[0] << 24
| buf[1] << 16
| buf[2] << 8
| buf[3] << 0;
For example,
uint32_t n;
unsigned char buf[4];
size_t bytes_read = fread (buf, 1, 4, stream);
if (bytes_read < 4) {
if (ferror(stream)) {
// Error
// ...
}
else if (feof(stream)) {
// Premature EOF
// ...
}
}
else {
n = buf[0] << 24
| buf[1] << 16
| buf[2] << 8
| buf[3] << 0;
}