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POSegmentation fault in reading a .dat file
 

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  1. POSegmentation fault in reading a .dat file
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    <p>Right now, I'm working on an example code that I wish to integrate into my program later. What essentially I'm trying to do is read a .dat file byte by byte and interpret the data (ie. interpret boot sector to output the sector size, reserved sectors etc.)</p> <p>To do this, I am reading the data byte by byte and, using the descriptions in fat12 of <a href="https://www.win.tue.nl/~aeb/linux/fs/fat/fat-1.html#ss1.3" rel="nofollow">https://www.win.tue.nl/~aeb/linux/fs/fat/fat-1.html#ss1.3</a> , I translate the data into the information that I want. Right now, I can pull individual bytes from the file (Is it right to assume that the data pulled is in hex?). However, I need two bytes to have something meaningful. So, I need to combine two bytes into one, convert the hex data into decimal and output the information. Unfortunately, right now, I'm getting a seg fault and for the life of me, I can't figure out what's wrong. Thanks in advance!</p> <p>int main (int argc, char **argv){</p> <pre><code>FILE *fp ,*fptest; long lSize; char *buffer; //Open file fptest= open("fat_volume.dat", "rb"); //Read file into buffer fread(buffer,1,512,fptest); //Parse the boot sector char tmpA, tmpB; tmpA = buffer[10]; //First byte tmpB = buffer[11]; //Second byte //Combine the two bytes into one char combinedBytes[3]; strcpy (combinedBytes, tmpA); strcat (combinedBytes, tmpB); //Hex to decimal converter long int li1; li1 = strtol (combinedBytes,NULL,16); printf ("The sector size is: %ld.\n", li1); return 0; </code></pre> <p>}</p>
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    1. COYou never `malloc` an array for `buffer`. Somewhere along the way, you need to say something like `buffer = malloc(512);`
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    2. COCan you please explain? My C is incredibly rusty. An example would be greatly appreciated!
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    3. COYou define yourself a `char*`, but you never point it at anything. It's probably pointing to some unknown location that could open a wormhole if you try to access it. You need to set it to point to some memory you own.
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