Help- command line hex edit tool

[DMCP2143]

I want to make a command line hex edit tool.
program.exe file.name hexAddress newByte

This works.

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#include <stdio.h>

int main ()
{   
    FILE *f = fopen( "Zelda3.sfc", "r+b" );
    fseek( f, 0x36D33, SEEK_SET );
    unsigned char newByte = 0x12;
    fwrite( &newByte, sizeof( newByte ), 1, f );
    fclose( f );
}

But arguments get me stumped. Best I have is this which compiles but does not work.

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#include <stdio.h>
#include <stdlib.h>

int main (int argc, char *argv[])  // program.exe file.name hexAddress newByte
{
    FILE *f = fopen( "argv[1]", "r+b" );
    int hexAddress = atoi( argv[2] );
    fseek( f, hexAddress, SEEK_SET );
    unsigned char newByte = atoi( argv[3] );
    fwrite( &newByte, sizeof( newByte ), 1, f );
    fclose( f );
}

Is this the place to ask for help? I want to make a bat file with my hex changes for notes and easy editing, maybe some toggle-able choices...

[KingMike]

One problem I immediately see is that you define "int".
I think it is the compiler which decides what an unspecified int size is.
But that could well be taken as a short signed int, which means you'd only be able to access bytes up to the first 32KB. (signed short int has a range -32k to +32k)

You want an unsigned long int (range 0 to 4GB).

[mziab]

Another obvious mistake is:

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FILE *f = fopen( "argv[1]", "r+b" );

Putting argv[1] in quotes makes it open a file named argv[1], not use the argument. Please remove the quotes around it and try again. There are a few other possible problems, but that seems like the most glaring one. Any particular reason you want to use C for this?

[DMCP2143]

Yep it was the quotes, I probably just should have slept on it.

Anyways, it won't take my hex values for input, it reads decimals then writes the hex equivilant. I sort of expected some issues here too.

[KingMike]

I've never heard of atoi before but Googling it, it seems to convert to decimal.

I write my own function to covert the string to hex, though I imagine there's probably already a C++ function for it.

[DMCP2143]

Yes I quickly googled hex command line argument and found it, here's the code for any who may be interested. It handles any hex values I give it, 0xFF, FF or ff, and reads 10 as decimal 16.

#include <stdio.h>
#include <stdlib.h>

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int main ( int argc, char *argv[] )  // program.exe file.name hexAddress newByte
{
    FILE *f = fopen( argv[1], "r+b" );
    long int hexAddress = ( long int ) strtol( argv[2], NULL, 16 );
    fseek( f, hexAddress, SEEK_SET );
    unsigned char newByte = ( unsigned char ) strtol( argv[3], NULL, 16 );
    fwrite( &newByte, sizeof( newByte ), 1, f );
    fclose( f );
}

[Lola814]

Yes I quickly googled hex command line argument and found it, here's the code for any who may be interested. It handles any hex values I give it,  0xFF, FF or ff, and reads 10 as decimal 16.

#include <stdio.h>
#include <stdlib.h>

Code Select Expand

int main ( int argc, char *argv[] )  // program.exe file.name hexAddress newByte
{
    FILE *f = fopen( argv[1], "r+b" );
    long int hexAddress = ( long int ) strtol( argv[2], NULL, 16 );
    fseek( f, hexAddress, SEEK_SET );
    unsigned char newByte = ( unsigned char ) strtol( argv[3], NULL, 16 );
    fwrite( &newByte, sizeof( newByte ), 1, f );
    fclose( f );
}

Ve never heard of atoi before but Googling it, it seems to convert to decimal.

I write my own function to covert the string to hex, though I imagine there's probably already a C++ function for it.