[metadata]
id = "ERR01-C"
type = "recommendation"
category = "ERR"
number = 1
title = "Use ferror() rather than errno to check for FILE stream errors"
description = """
Useferror()rather thanerrnoto check whether an error has occurred on a file
stream (for example, after a long chain ofstdiocalls). Theferror()function tests
the error indicator for a specified stream and returns nonzero if and only if
the error indicator is set for the stream. Manyimplementationsof thestdiopackage
adjust their behavior slightly ifstdoutis a terminal. To make the determination,
these implementations perform some operation that fails (withENOTTY) ifstdoutis
not a terminal. Although the output operation goes on to complete
successfully,errnostill containsENOTTY. This behavior can be mildly confusing,
but it is not strictly incorrect because it is meaningful for a program to
inspect the contents oferrnoonly after an error has been reported. More
precisely,errnois meaningful only after a library function that setserrnoon
error has returned an error code. errno = 0; printf("This\n"); printf("is\n");
printf("a\n"); printf("test.\n"); if (errno != 0) { fprintf(stderr, "printf
failed: %s\n", strerror(errno)); }
"""
severity = "Low"
likelihood = "Probable"
priority = "P6"
level = "L2"
cert_version = "2016 Edition (Wiki)"
last_modified = "May 20, 2025"
[rules.cert_c.ERR01-C]
enabled = true
[references]
wiki = "https://wiki.sei.cmu.edu/confluence/display/c/ERR01-C.+Use+ferror%28%29+rather+than+errno+to+check+for+FILE+stream+errors"