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I'm doing CS50 (Week 4 Lab 4 Volume) and I have to copy a header from an input WAV file to output file (the 44 first bytes).

To start, I created the array uint8_t header[HEADER_SIZE];. Then, I used fread. But why the right solution is : fread(header, HEADER_SIZE, 1, input); and not something like : fread(header, sizeof(uint8_t), HEADER_SIZE, input);?

Don't it mean that all the header will be copied at once in the header array in a single element (which will lead to an error since an element must have 1 byte due to its type uint8_t)? Does the compiler now how to handle the situation when reading at once many bytes into an array with only 1 byte per element?

Thank you!

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    It could be. But here you need to read the whole header, so the element size is HEADER_SIZE and the number of elements is 1. The difference is that on success, fread with return 1 and HEADER_SIZE respectively. Commented Jun 27, 2022 at 9:30
  • Who says the second one is wrong? Did you try it? Commented Jun 27, 2022 at 9:31
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    You can read 1 item of size HEADER_SIZE or HEADER_SIZE items of size 1. What's the difference in the end? Besides of course, return value of fread will be different. Commented Jun 27, 2022 at 9:31
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    The bytes read from the file will not be stored in the first element but within the whole array. Commented Jun 27, 2022 at 9:49
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    Note that sizeof(char) is always 1 (by definition). So, using it in calculations is deprecated. A little tricky with sizeof(uint8_t) but don't use for the same reason. Strictly speaking, fread(header,sizeof(header),1,input) might be the best, but ... In glibc [linux], the size and nmemb are multiplied together as the first line of fread: size_t bytes_requested = size * count; and that is used internally. So, it's a bit of a moot point. read (the syscall) uses a byte count, so I do: fread(header,1,sizeof(header),input) to get a byte count return value Commented Jun 27, 2022 at 15:51
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