What is the rationale for fread/fwrite taking size and count as arguments?

c libc
David Holm picture David Holm · Nov 17, 2008 · Viewed 27.5k times · Source

We had a discussion here at work regarding why fread and fwrite take a size per member and count and return the number of members read/written rather than just taking a buffer and size. The only use for it we could come up with is if you want to read/write an array of structs which aren't evenly divisible by the platform alignment and hence have been padded but that can't be so common as to warrant this choice in design.

From FREAD(3):

The function fread() reads nmemb elements of data, each size bytes long, from the stream pointed to by stream, storing them at the location given by ptr.

The function fwrite() writes nmemb elements of data, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr.

fread() and fwrite() return the number of items successfully read or written (i.e., not the number of characters). If an error occurs, or the end-of-file is reached, the return value is a short item count (or zero).

Answer

Peter Miehle picture Peter Miehle · Nov 17, 2008

The difference in fread(buf, 1000, 1, stream) and fread(buf, 1, 1000, stream) is, that in the first case you get only one chunk of 1000 bytes or nuthin, if the file is smaller and in the second case you get everything in the file less than and up to 1000 bytes.

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