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Erlang Interface
Reference Manual
Version 3.7.13

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# erl_error

### C LIBRARY

erl_error

### LIBRARY SUMMARY

Error Print Routines

### DESCRIPTION

This module contains some error printing routines taken from Advanced Programming in the UNIX Environment by W. Richard Stevens.

These functions are all called in the same manner as printf(), i.e. with a string containing format specifiers followed by a list of corresponding arguments. All output from these functions is to stderr.

### EXPORTS

void erl_err_msg(FormatStr, ... )

Types:

const char *FormatStr;

The message provided by the caller is printed. This function is simply a wrapper for fprintf().

void erl_err_quit(FormatStr, ... )

Types:

const char *FormatStr;

Use this function when a fatal error has occurred that is not due to a system call. The message provided by the caller is printed and the process terminates with an exit value of 1. The function does not return.

void erl_err_ret(FormatStr, ... )

Types:

const char *FormatStr;

Use this function after a failed system call. The message provided by the caller is printed followed by a string describing the reason for failure.

void erl_err_sys(FormatStr, ... )

Types:

const char *FormatStr;

Use this function after a failed system call. The message provided by the caller is printed followed by a string describing the reason for failure, and the process terminates with an exit value of 1. The function does not return.

### Error Reporting

Most functions in erl_interface report failures to the caller by returning some otherwise meaningless value (typically NULL or a negative number). As this only tells you that things did not go well, you will have to examine the error code in erl_errno if you want to find out more about the failure.

### EXPORTS

volatile int erl_errno

erl_errno is initially (at program startup) zero and is then set by many erl_interface functions on failure to a non-zero error code to indicate what kind of error it encountered. A successful function call might change erl_errno (by calling some other function that fails), but no function will ever set it to zero. This means that you cannot use erl_errno to see if a function call failed. Instead, each function reports failure in its own way (usually by returning a negative number or NULL), in which case you can examine erl_errno for details.

erl_errno uses the error codes defined in your system's <errno.h>.

Note

Actually, erl_errno is a "modifiable lvalue" (just like ISO C defines errno to be) rather than a variable. This means it might be implemented as a macro (expanding to, e.g., *_erl_errno()). For reasons of thread- (or task-)safety, this is exactly what we do on most platforms.