Thread: Reading 16 bit binary numbers from file

This is supposed to read a series of 16 bit binary numbers as short ints in the array memory. However, it only appears to be reading the first number, and I can't figure why.

Code:

short int memory[256];

void readFile(){
    //read input file into int memory[]
    FILE *ifp;
    ifp = fopen("proj1a.dat", "r"); //input file 
    
    //validates file exists
    if (ifp == NULL)
    {
        perror("proj1a.dat");
        exit(0);
    }
       
    char str[16];//current line from file 
    int i = 0; //index of memory
    while(fgets(str, 17, ifp)){
        memory[i] = (short)(strtol(str, NULL, 2));
        printf("%d\n", memory[i]);//DEBUG
        i++;
    }
}

Please post a small sample of your input file.

Also post a sample of what your program is outputting and what you expect the program to output.


Jim

What exactly do you mean when you say "16 bit binary numbers"? If you have a string like "123" then strtol can convert that to the integer 123 but strtol does not handle 16 bit code points. If it's just 16 bit binary numbers you want to read then use fread with a pointer to your memory buffer. If it's a text file encoded as UTF-16 or similar then it gets a bit more tricky. If wchar_t is 16 bits on your platform then you can use fgetws and wstrol but otherwise you'll need to read the raw binary data with fread and implement the string to number conversion yourself.

Sample input:
0000000000001010
0001000000001000
0000000100001011

Expected output:
10
4104
267

Actual output:
10

@MOS: The third parameter for strtol is the base, which I set to 2. Reading the binary numbers appears to be working correctly, its just that it only does it once instead of continuing.

Thank you, this works. Changing the size of str to anything less than 18 gives a completely wrong output. Could anyone explain why this is the case? Each line of the input file has 16 chars, so I would expect str to only need to be 16 chars long.

Code:

void readFile(){
    //read input file into int memory[]
    FILE *ifp;
    ifp = fopen("proj1a.dat", "r"); //input file TODO: change to "../instr/proj1a.dat" before submitting
    
    //validates file exists
    if (ifp == NULL)
    {
        perror("proj1a.dat");
        exit(0);
    }
       
       char str[18] = {0};//current line from file 
       int i = 0; //index of memory
    while(fgets(str, sizeof(str), ifp) != NULL){
        memory[i] = (short)(strtol(str, NULL, 2));
        printf("%d\n", memory[i]);//DEBUG
        i++;
    }
}

So why doesn't fgets(str, 16, ifp) just get the first 16 characters?

Because fgets() always reserves room for the end of string character, meaning it will retrieve only 15 actual characters from the file, if your limit is 16. Your fgets call will retrieve "000100010001000" and append the end of string character to the string. This will leave these characters in the file: "1\n" for the next extraction operation.

By the way the end of string character is not found inside a text file.

Jim