Thread: How to parse my buffer by size?

  1. #1
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    Jan 2018
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    How to parse my buffer by size?

    Hello.

    I need your help.

    I have a buffer (there are my data from binary file)
    Code:
    char *buffer;
    And I know lenght of buffer (it is size of my binary file)
    Code:
    unsigned long Len;
    The length of buffer is variable. For example 100Bytes to 2048Kbytes.

    And I need function, to generate array with specific size (for example, specific size):
    Code:
    size_t maxSize = 4096;
    But I don't know, how to generate array with data, parse by size.

    For example:
    Binary file is 8168Bytes. I create buffer with data, lenght LEN. And I need parse buffer by size. So I need output:
    OUT1 .... size 4096Bytes
    OUT2 .... size 4072Bytes

    Or
    Binary file is 100Bytes. I create buffer with data, lenght LEN. And I need parse buffer by size. So I need output:
    OUT1 .... size 100Bytes

    Or
    Binary file is 11560Bytes. I create buffer with data, lenght LEN. And I need parse buffer by size. So I need output:
    OUT1 .... size 4096Bytes
    OUT2 .... size 4096Bytes
    OUT3 .... size 3368Bytes

    Can anybody help me, with solution?

  2. #2
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    And I have this function. And this function create xy files from one file by size.

    Code:
    int splitFile(char *fileIn, size_t maxSize)
    {
        int result = 0;
        FILE *fIn;
        FILE *fOut;
        char buffer[1024 * 16];
        size_t size;
        size_t read;
        size_t written;
    
        if ((fileIn != NULL) && (maxSize > 0))
        {
            fIn = fopen(fileIn, "rb");
            if (fIn != NULL)
            {
                fprintf(stderr, "\n");
                fOut = NULL;
                result = 1;   /* we have at least one part */
    
    
                while (!feof(fIn))
                {
                    /* initialize (next) output file if no output file opened */
                    if (fOut == NULL)
                    {
                        sprintf(buffer, "%s.%03d", fileIn, result);
                        fprintf(stderr, "%s.%03d\n", fileIn, result);
    
                        fOut = fopen(buffer, "wb");
                        if (fOut == NULL)
                        {
                            result *= -1;
                            break;
                        }
    
                        size = 0;
                    }
    
                    /* calculate size of data to be read from input file in order to not exceed maxSize */
                    read = sizeof(buffer);
                    if ((size + read) > maxSize)
                    {
                        read = maxSize - size;
                    }
    
                    /* read data from input file */
                    read = fread(buffer, 1, read, fIn);
                    if (read == 0)
                    {
                        result *= -1;
                        break;
                    }
    
                    /* write data to output file */
                    written = fwrite(buffer, 1, read, fOut);
                    if (written != read)
                    {
                        result *= -1;
                        break;
                    }
    
                    /* update size counter of current output file */
                    size += written;
                    if (size >= maxSize)   /* next split? */
                    {
                        fclose(fOut);
                        fOut = NULL;
                        result++;
                    }
                }
                fprintf(stderr, "\n");
                /* clean up */
                if (fOut != NULL)
                {
                    fclose(fOut);
                }
                fclose(fIn);
            }
        }
    
    
        return (result);
    }
    And how to modificate, to return x, y, z array with data?

  3. #3
    C++ Witch laserlight's Avatar
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    Is maxSize really only known at run time, or can it be a compile time constant? If it can be the latter, then I recommend:
    Code:
    #define BUFFER_MAXSIZE 4096
    
    /* ... */
    
    char buffer[BUFFER_MAXSIZE];
    This way, you avoid dynamic memory location, and since a buffer's maximum size is likely to be relatively small, this should be perfectly fine as a non-static local variable. If maxSize is only known at run time, then using malloc and free would be appropriate, except that as an optimisation you would only call malloc once or twice: once if you only use the buffer once; twice if you use the buffer more than once, i.e., once on the first use, once on the last use.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  4. #4
    and the hat of int overfl Salem's Avatar
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    Are you trying to return all the generated filenames, in addition to the number of files generated?

    Your use of feof is incorrect. If your input file is an exact multiple of maxSize, you end up with an empty last file.

    What happens when you split an empty file?
    What happens when you have more than 1000 parts?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  5. #5
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    Cant you just copy the elements you want to parse into other arrays?

    binarydata[1000]
    data1[max_size];
    data2[max_size];

  6. #6
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    Expanding on my answer above

    If you want to parse binarydata to two other arrays


    &ptr1=binarydata[75] //point at where the array will be parsed

    //put this in a for loop to assign elements
    data1[i]=*(ptr1++);


    //then do it again for the other parse data set
    &ptr1=binarydata[10]

    //put this in a for loop to assign elements
    data2[i]=*(ptr1++);

  7. #7
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    Split, as one of the GNU coreutils, has been hacked/polished for 30 years. (split.c source) Or you might look at GBufferedInputStream in glib GIO.

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