CODEWITHSUNDEEP
c
Juan Montoya
Juan Montoya

Reputation: 96

Write binary file C from unsigned char

I'm making a program that writes a binary file, the content of this binary file are in an unsigned char pointer. The next code is the way that I using to generate the binary

while (f > 0) {
    oct = (unsigned char) *datosOct->informacion++;

    for (int i = 2; i >= 0; --i)
    {   
        char actual = ((oct & (1 << i)) ? '1' : '0');
        temporal = appendCharToCharArray(temporal, actual);
    }           
    f--;
}
datosBin->informacion = (unsigned char*)temporal;

I had used fopen in mode wb, but it literals write a file with 1s and 0s. this is the function that I use to write (I using the default compiler of Visual Studio). I use the next code to write the file

file = fopen(nombreArchivo, "wb");
fwrite(datosBin->informacion, sizeof(char), archivoEnOctal->tamanio, file);

My starting point is a char array that contains '1's and '0's, each byte of '1's and '0's represents an ASCII value. For example, '1010000' is the ASCII 80 representing the letter 'P', if I transforms the binary char array ('1010000') to an array of chars ('P') when it finds values whose ASCII is 00 takes them as the end of the text and does not write them to the final file. One of the possible outputs of my code is an image, so I need to write these values 00. I tried this to write the chars directly, but this doesn't work for the images for the reason I mentioned before

while (f > 0) {
    oct = (unsigned char) *datosOct->informacion++;

    for (int i = 2; i >= 0; --i)
    {   
        if (size == 8) {
            size = 0;
            char nuevaLetra = strtol(temporal, 0, 2); 
            if (nuevaLetra == 00) {
                nuevaLetra = '\0';
                //nuevaLetra = (char) 0;
            }
            response = appendCharToCharArray(response, nuevaLetra);
            temporal = (char*)"";
        }
        size++;
        char actual = ((oct & (1 << i)) ? 1 : 0);
        temporal = appendCharToCharArray(temporal, actual);
    }           
    f--;
}

Upvotes: 0

Views: 626

Answers (1)

enhzflep
enhzflep

Reputation: 13089

I'll leave it to you to build and run it, before looking inside output.txt

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

typedef struct
{
    unsigned char data;
    unsigned char numBitsValid;
} bitAccumalator_t;

int main()
{
    FILE *fp = fopen("output.txt", "wb");
    char *inputStream = "011001000110111101100101011100110010000001110100011010000110100101110011001000000110100001100101011011000111000000111111";
    int numBits = strlen(inputStream);
    bitAccumalator_t outBuffer = {0,0};
    for (int i=0; i<numBits; i++)
    {
        outBuffer.data <<= 1;
        if (inputStream[i] == '1')
        {
            outBuffer.data |= 1;
        }
        outBuffer.numBitsValid++;

        if (outBuffer.numBitsValid == 8)
        {
            fwrite(&outBuffer.data, 1, 1, fp);
            outBuffer.data = 0;
            outBuffer.numBitsValid = 0;
        }
    }
    fclose(fp);
    return 0;
}

Upvotes: 3

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