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when I read from a file using fread (C language), the return value of fread sometimes would be 0.
As manual suggested:
fread() and fwrite() return the number of items successfully read or written
do I have to write code like this?
int bytes_read;
while((bytes_read = fread(buffer, sizeof(int), 1, fp)) == 0) {
}
do we always have to check whether fread or fwrite succeeded?
664
If fread returns fewer than the requested number of records, you've either hit EOF or a serious read error. You can distinguish between them by checking feof() and ferror() . Similarly, if fwrite returns fewer than the requested number of records, you've either run out of disk space or hit a serious write error.
The fwrite() function returns the number of members successfully written, which may be less than nitems if a write error is encountered. If size or nitems is 0, fwrite() returns 0 and the state of the stream remains unchanged.
The function fread() reads nmemb items 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 items of data, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr.
The fread() function returns the number of full items successfully read, which can be less than count if an error occurs, or if the end-of-file is met before reaching count. If size or count is 0, the fread() function returns zero, and the contents of the array and the state of the stream remain unchanged.
No, there's no sense in doing a retry-loop like this if fread or fwrite returns fewer than the expected number of records read or written. That is to say, stdio is not like the low-level read and write operations that can result in "short" reads or writes.
If fread returns fewer than the requested number of records, you've either hit EOF or a serious read error. You can distinguish between them by checking feof() and ferror().
Similarly, if fwrite returns fewer than the requested number of records, you've either run out of disk space or hit a serious write error.
In any case, due to buffering stdio makes it essentially impossible to know how much was successfully written, so if you encounter a write error, you usually need to consider the file lost and abort the whole operation.
169
http://pubs.opengroup.org/onlinepubs/000095399/functions/fread.html
Upon successful completion, fread() shall return the number of elements successfully read which is less than nitems only if a read error or end-of-file is encountered. If size or nitems is 0, fread() shall return 0 and the contents of the array and the state of the stream remain unchanged. Otherwise, if a read error occurs, the error indicator for the stream shall be set, and errno shall be set to indicate the error.
http://pubs.opengroup.org/onlinepubs/007904875/functions/fwrite.html
The fwrite() function shall return the number of elements successfully written, which may be less than nitems if a write error is encountered. If size or nitems is 0, fwrite() shall return 0 and the state of the stream remains unchanged. Otherwise, if a write error occurs, the error indicator for the stream shall be set,and errno shall be set to indicate the error
The ferror() or feof() functions must be used to distinguish between an error condition and an end-of-file condition.
3
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