Error Functions

Header file

• errno.h contains the definition of the errno variable
• stdio.h contains the function prototype for the perror function
• string.h contains the function prototype for the strerror function

Error Condition - errno

• extern int errno or #define errno definition is used to hold implementation-defined error codes from standard library routines
• All error codes are positive integers and are traditionally defined in <errno.h>
• errno contains the last error condition which occurred; library functions should never clear errno, so if errno is to be checked after a library call, it is the programmer's responsibility to set it to 0 before calling the library routine

Error String - strerror

• char *strerror(int errnum)
  • strerror returns a pointer to the error message string associated with errnum

Print Error String - perror

• void perror(const char *str)
  • perror finds the error message string associated with the global errno variable and prints it, prepended by the text in str and a colon if str is non-null, and followed by a newline, to the standard error file descriptor.

List of Common Error Constants

EPERM

Operation not permitted

ENOENT

No such file or directory

ESRCH

No such process

EINTR

Interrupted system call

EIO

I/O error

ENXIO

No such device or address

E2BIG

Argument list too long

ENOEXEC

Exec format error

EBADF

Bad file descriptor

ECHILD

No child processes

ENOMEM

Not enough core

EACCES

Permission denied

EFAULT

Bad address

ENOTBLK

Block device required

EBUSY

Resource busy

EEXIST

File exists

EXDEV

Cross-device link

ENODEV

No such device

ENOTDIR

Not a directory

EISDIR

Is a directory

EINVAL

Invalid argument

ENFILE

Too many open files in system

EMFILE

Too many open files

ENOTTY

Inappropriate I/O control operation

ETXTBSY

Text file busy

EFBIG

File too large

ENOSPC

No space left on device

ESPIPE

Illegal seek

EROFS

Read-only file system

EMLINK

Too many links

EPIPE

Broken pipe

EDOM

Numerical argument out of domain

ERANGE

Result too large

ENOMSG

No message of desired type

EIDRM

Identifier removed

ECHRNG

Channel number out of range

ELNRNG

Link number out of range

EUNATCH

Protocol driver not attached