Reading parts of a file and writing it to single unsigned char

Question

I want to read from few parts of a file and than output it as one unsigned char. This is a simplified version of this:

void loadPartsOfFile (const char *filename, unsigned char **output)
{
    *output = malloc(333);

    FILE *file = fopen(filename, "rb");
    fseek(file, 0, SEEK_SET); 
    fread(*output, 1, 111, file);
    fseek(file, 10254, SEEK_SET);
    fread(*output, 1, 222, file);

    fclose(file);
}

Second fread just overwrites what first added to output. Is there a way to append second data stream to output?

score 2 · Accepted Answer · answered Apr 15 '12 at 16:58

2

void loadPartsOfFile (const char *filename, unsigned char **output)
{
    *output = realloc(*output, 333);

    FILE *file = fopen(filename, "rb");
    fseek(file, 0, SEEK_SET); 
    fread(*output, 1, 111, file);
    fseek(file, 10254, SEEK_SET);
    fread(*output+111, 1, 222, file);

    fclose(file);
}

answered Apr 15 '12 at 16:58

wildplasser

43,142
8
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109

Thank you! By the way is there a way to add to output some data like: char data[2] = {0xD5,0x48}; – Martin Apr 15 '12 at 21:41
Yes, of course. Just increment the size for realloc by 2, and do a `memcpy(*output+some_offset, data, 2);` somewhere. If the data is inserted before the other two members, these will have to be shifted up too. – wildplasser Apr 16 '12 at 10:22

score 2 · Answer 2 · answered Apr 15 '12 at 17:00

2

Just increment *output until the end of the previous read, i. e. *output + 111.

answered Apr 15 '12 at 17:00

Sebastian

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34
58

Reading parts of a file and writing it to single unsigned char

2 Answers2