Find pattern in binary file?

Question

I wrote the function below to find a pattern in a text:

bool match(char* patt,char* text){ 

    int textLoc=0, pattLoc=0, textStart=0;  

    while(textLoc < (int) strlen(text) && pattLoc < (int)strlen(patt)){ 

        if( *(patt+pattLoc) == *(text+textLoc) ){     
            textLoc= textLoc+1;          
            pattLoc= pattLoc+1;      
        }   
        else{          
            textStart=textStart+1;  
        textLoc=textStart;           
        pattLoc=0;   
        }     
    }   


    if(pattLoc >=    (int) strlen(patt)) 
        return true;  
    else return false; 

}

As it appears, the function takes two parameters of the type char*. I would like to use this function to find a pattern in a binary file, what you suggest to carry out this issue?

By binary file, are you mapping the file into memory yourself or are you loading it then injecting a DLL to it? — Mike Kwan
– Mike Kwan, Commented Mar 10, 2012 at 12:42
@ Mike Kwan Yes I am going to map the file in the memory by CreateFilemMapping .. etc. — Aan
– Aan, Commented Mar 10, 2012 at 16:14
Consider what would happen if your binary file contained no null bytes. You can't treat a binary stream of data as null-terminated char strings. — Carey Gregory
– Carey Gregory, Commented Mar 10, 2012 at 22:39

Nuno_147 · Accepted Answer · 2012-03-10 08:09:42Z

1

There is no right or wrong here. The only difference I would consider here is to use buffer/size approach instead of strings.

You should also consider how you would like to read the file. Are you going to read the entire file to memory or are you going to read it in sections ?

If you are going to read it in sections, always save the last part of each section ( the size of your search pattern ) and append it to the beginning of your next section. This way the cuts-off for each section will be evaluated as well.

answered Mar 10, 2012 at 8:09

Nuno_147

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Comments

Roland Illig · Accepted Answer · 2012-03-10 08:10:04Z

1

It seems to me that you tried to implement the popular strstr function on your own. But that will not help you, since you asked for finding a binary pattern. The function you should use in that case is called memmem.

answered Mar 10, 2012 at 8:10

Roland Illig

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2 Comments

Aan Over a year ago

Is it for linux? I use Windows.

Roland Illig Over a year ago

You're right, the memmem function is not available everywhere. But there is a good and simple implementation from the git project, called gitmemmem. You can use that instead of doing it yourself.

Chibueze Opata · Accepted Answer · 2012-03-10 08:41:30Z

1

You sound more like you are looking for the best way to find patterns in files. If so, there is a very good document for single and multiple pattern checking:

Given a pattern P = a1a2...an, Fnd all occurrences of P in a text T = b1b2...bm.

Extension to multipattern cases: Given a set of patterns, P1, P2, ..., Pl ,

Fnd all occurrences of P in a text T = b1b2...bm.

You can check this document for simple explanation and this one for more detailed and different implementations/codes.

edited Mar 10, 2012 at 8:41

answered Mar 10, 2012 at 8:20

Chibueze Opata

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1 Comment

Chibueze Opata Over a year ago

@Adban sorry. Updated links now.

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