Question

Basically I have a buffer in which i am looking for various flags to read certain fields from a binary file format. I have file read into a buffer but as i started to write code to search the buffer for the flags i immediately hit a wall. I am a C++ noob, but here is what i have:

void FileReader::parseBuffer(char * buffer, int length)
{
  //start by looking for a vrsn
  //Header seek around for a vrns followed by 32 bit size descriptor
  //read 32 bits at a time
  int cursor = 0;
  char vrsn[4] = {'v','r','s','n'};
  cursor = this->searchForMarker(cursor, length, vrsn, buffer);
}

int FileReader::searchForMarker(int startPos, int eof, char marker[], char * buffer)
{
  int cursor = startPos;
  while(cursor < eof) {
    //read ahead 4 bytes from the cursor into a tmpbuffer
    char tmpbuffer[4] = {buffer[cursor], buffer[cursor+1], buffer[cursor+2], buffer[cursor+3]}; 
    if (strcmp(marker, tmpbuffer)) {
      cout << "Found: " << tmpbuffer;
      return cursor;
    }
    else {
      cout << "Didn't Find Value: " << marker << " != " << tmpbuffer;
    }
    cursor = cursor + 4;
  }
}

my header looks like this:

#ifndef __FILEREADER_H_INCLUDED__
#define __FILEREADER_H_INCLUDED__

#include <iostream>
#include <fstream>
#include <sys/stat.h>



class FileReader {
  public:
    FileReader();
    ~FileReader();
    int open(char *);
    int getcode();
  private:
    void parseBuffer(char *, int);
    int searchForMarker(int, int, char[], char *);
    char *buffer;
};

#endif

I would expect to get back a match for vrsn with strcmp but my result looks like this

Didn't Find Value: vrsn != vrsn
Found: 

It looks like it finds it on the second pass after its passed the char array i am looking for.

Relevant hexcode

Answer 1

Shouldn’t that be something like int FileReader::searchForMarker(...) { .... }?

For the second query, I guess the strcmp works when it has two null terminated strings as its arguments. For example str1[]="AAA"; and str2[]="AAA"; then strcmp() would be used as
if(strcmp(str1,str2)==0) which will return 0 to indicate that they are equal. In your case, the tmpbuffer that you have created is not a null terminated string unless you add \0 in the end.So you might want to add \0 in the end of your tmpbuffer to create a string of 'v' 'r' 'n' 's'.