Hex value comparison and save to file C++ - c++

Question

I am reading H.264 bitstream as Hex file in c++. I want to insert some string whenever some certain condition met.Like in the attached image if hex value of 00 00 00 01 occurs anywhere in the file i want to add some string like ABC before 00 00 00 01 in the file and save this as a new file. Write now my approach is to read h.264 file as hex. convert it into string and make a string comparison. if there is a way i can do a straight hex comparison? Here is my current code
#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <iomanip>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
unsigned char x;
string s1,s2,s3;
s2="Mushahid Hussain";
s3="0000000141";
std::ifstream input("d:\\Jm\\videos\\trying2.264", std::ios::binary);
input >> std::noskipws;
while (input >> x) {
long constant = 0x0000000168;
std::ostringstream buffer;
buffer << std::hex << std::setw(2) << std::setfill('0')
<< (int)x;
s1=buffer.str();
if (s1.find(s1) != std::string::npos) {
cout<<"hello";
s1+=s2;
}
std::ofstream outfile;
outfile.open("d:\\Jm\\bin\\trying5.264", std::ios_base::app);
outfile << s1;
}
return 0;
}
Edit 1
As answered by Tommylee2k i am able to append string . But problem is that at the end of file hex CD value is appending like shown in the attached image.

Answer 1

perhaps a better approach is to read the file binary into a memory buffer, and find the memcmp() instead.
When you found your pattern, you write the block ahead of the match, then your "ABC"-string, and continue searching the rest of the file
#include <stdio.h>
#include <string.h>
#include <memory.h>
#include <malloc.h>
char pattern[4]= { 0x00,0x00,0x01,0x67 };
char *memfind(char *s, int len, char *p, int plen) {
int n=0;
char *pos = s;
while ((pos-s)<(len-plen)) {
while ( *(pos+n) == *(p+n) && n<=plen) n++;
if (n==plen)
return pos;
pos++;n=0;
}
return NULL;
}
int main() {
FILE *in = fopen("in.vid", "r+");
FILE *out = fopen("out.vid", "wb");
// get Filesize
size_t size = 0;
fseek(in, 0L, SEEK_END);
size = ftell(in);
// read whole file in
char *buffer = malloc(size);
fseek (in, 0L, SEEK_SET);
fread (buffer, size, 1, in);
char *currentPos = buffer;
char *found;
if (buffer) {
while (1) {
found = memfind(currentPos, size-(currentPos-buffer), pattern, sizeof(pattern));
if (found==NULL) break;
fwrite(currentPos, 1, (size_t) (found-currentPos), out);
fwrite("ABC", sizeof("ABC"), 1, out);
fwrite(pattern, sizeof(pattern),1,out);
currentPos=found+4;
}
fwrite (currentPos, 1, (size_t) size - (currentPos-buffer), out);
free(buffer);
}
fclose (in);
fclose (out);
return 0;
}