Creideiki <[email protected]> added the comment:
I ran this program:
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
void print(const char *s, size_t l)
{
errno = 0;
fwrite(s, l, 1, stdout);
int saved_errno = errno;
fprintf(stderr,
"After \"%s\": ferror(): %i, strerror(): %s\n",
s, ferror(stdout), strerror(saved_errno));
clearerr(stdout);
}
int main()
{
usleep(5 * 1000 * 1000);
print("A", 1);
print("\n", 1);
print("B\nC", 3);
print("\n", 1);
print("D", 1);
print("\n", 1);
return 0;
}
Got this result:
write(2, "After \"A\": ferror(): 0, strerror(): Success\n", 44) = -1 EIO
(Input/output error)
write(1, "A\n", 2) = -1 EIO (Input/output error)
write(2, "After \"\n\": ferror(): 1, strerror(): Input/output error\n", 55) =
-1 EIO (Input/output error)
write(1, "B\n", 2) = -1 EIO (Input/output error)
write(2, "After \"B\nC\": ferror(): 1, strerror(): Input/output error\n", 57) =
-1 EIO (Input/output error)
write(1, "\n", 1) = -1 EIO (Input/output error)
write(2, "After \"\n\": ferror(): 1, strerror(): Input/output error\n", 55) =
-1 EIO (Input/output error)
write(2, "After \"D\": ferror(): 0, strerror(): Success\n", 44) = -1 EIO
(Input/output error)
write(1, "D\n", 2) = -1 EIO (Input/output error)
write(2, "After \"\n\": ferror(): 1, strerror(): Input/output error\n", 55) =
-1 EIO (Input/output error)
So, fwrite() with a string which does not contain a newline is buffered and
ferror() returns 0. fwrite() with a string which does contain a newline, in the
middle or at the end, flushes the buffer and makes ferror() return 1.
I think this means that after print('A') gets turned into write(1, "A\n", 2),
ferror() should still be 1.
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<https://bugs.python.org/issue32345>
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