errc(3bsd) 3bsd errc(3bsd)

# [NAME](#NAME)

`errc`, `verrc`, `warnc`, `vwarnc` — formatted error messages

# [LIBRARY](#LIBRARY)

library “libbsd”

# [SYNOPSIS](#SYNOPSIS)

`#include <err.h>` (See [libbsd(7)](/man/os/libbsd/libbsd.7) for include usage.)  
`void`  
`errc`(`int status`, `int code`, `const char *fmt`, `...`);

`void`  
`verrc`(`int status`, `int code`, `const char *fmt`, `va_list args`);

`void`  
`warnc`(`int code`, `const char *fmt`, `...`);

`void`  
`vwarnc`(`int code`, `const char *fmt`, `va_list args`);

# [DESCRIPTION](#DESCRIPTION)

The [`err`](#err)() and [`warn`](#warn)() family of functions display a formatted error message on the standard error output. In all cases, the last component of the program name, followed by a colon (‘:’) character and a space, are output. The text that follows depends on the function being called. The `fmt` specification (and associated arguments) may be any format allowed by [printf(3)](/man/os/libbsd/printf.3) or `NULL`. If the `fmt` argument is not `NULL`, the formatted error message is output.

The functions all output an error message string affiliated with an error value (see [strerror(3)](/man/os/libbsd/strerror.3)), preceded by a colon character and a space if `fmt` is not `NULL`. That is, the output is as follows:

```
progname: fmt: error message string
```

if `fmt` is not `NULL`, or:

```
progname: error message string
```

if it is.

The argument `code` is used as the error value instead of the current value of the global variable `errno`.

In all cases, the output is followed by a newline character.

The [`errc`](#errc)(), and [`verrc`](#verrc)() functions do not return, but exit with the value of the argument `status`.

# [EXAMPLES](#EXAMPLES)

Display the current `errno` information string and exit:

```
if ((p = malloc(size)) == NULL)
	err(1, NULL);
if ((fd = open(file_name, O_RDONLY, 0)) == -1)
	err(1, "%s", file_name);
```

Display an error message and exit:

```
if (tm.tm_hour < START_TIME)
	errx(1, "too early, wait until %s", start_time_string);
```

Warn of an error:

```
if ((fd = open(raw_device, O_RDONLY, 0)) == -1)
	warnx("%s: %s: trying the block device",
	    raw_device, strerror(errno));
if ((fd = open(block_device, O_RDONLY, 0)) == -1)
	err(1, "%s", block_device);
```

# [SEE ALSO](#SEE_ALSO)

[err(3)](/man/os/libbsd/err.3) [exit(3)](/man/os/libbsd/exit.3), [perror(3)](/man/os/libbsd/perror.3), [printf(3)](/man/os/libbsd/printf.3), [strerror(3)](/man/os/libbsd/strerror.3)

# [HISTORY](#HISTORY)

The functions `errc`(), `verrc`(), `warnc`(), and `vwarnc`() first appeared in FreeBSD 3.0, NetBSD 7.0 and OpenBSD 5.6.

# [CAVEATS](#CAVEATS)

It is important never to pass a string with user-supplied data as a format without using ‘`%s`’. An attacker can put format specifiers in the string to mangle the stack, leading to a possible security hole. This holds true even if the string has been built “by hand” using a function like `snprintf`(), as the resulting string may still contain user-supplied conversion specifiers for later interpolation by the `err`() and `warn`() family of functions.

Always be sure to use the proper secure idiom:

```
errc(1, 0, "%s", string);
```

April 23, 2014 Linux 4.19.0-gvisor

---

Document: verrc(3bsd) from libbsd 0.12.2-r11 (Chainguard OS)
Source: https://gitlab.freedesktop.org/libbsd/libbsd