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Top Forums Programming Small query regarding function "char * strerror(int errnum)" Post 302762859 by JohnGraham on Tuesday 29th of January 2013 06:14:24 AM
Old 01-29-2013
Quote:
Originally Posted by Praveed_218
The MAN page tells under the BUG section that "For unknown error numbers, the strerror() function will return its result in a static buffer which may be overwritten by subsequent calls."
Quote:
Originally Posted by Praveen_218
The primary reason to ask this query is because of the fact that the MAN pages themselves not making me sure if the programmer needs to handle any kind of cleanup post calling strerror()?
The man page tells you that the result may be in a static buffer. It tells you this to let you know two things:
  1. You do not need to free the result returned from this function. A static buffer (as in when you use "static" within a function) exists throughout the lifetime of the program and does not need to be released by anyone.
  2. You should not rely on the result being available over multiple calls to strerror(), as in:
    Code:
    char *err1 = strerror(errno);
    some_call();
    char *err2 = strerror(errno);
    printf("Got errors %s and %s\n", err1, err2);

    This is because it's possible that the result of both calls to strerror() will be a pointer to the same (static) buffer.

Some advice: When asking questions on forums, ask what you really want to ask, as opposed to second-guessing what you want. When you ask where the result of strerror() will be and if you can edit it, my first instinct is to just say "no, don't do any of that forget about it!", but if you just ask whether you should free() the result and why the man page mentions a static buffer, you'll get a much better response.
 

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strerror(3C)						   Standard C Library Functions 					      strerror(3C)

NAME
strerror, strerror_r - get error message string SYNOPSIS
#include <string.h> char *strerror(int errnum); int strerror_r(int errnum, char *strerrbuf, size_t buflen); DESCRIPTION
The strerror() function maps the error number in errnum to an error message string, and returns a pointer to that string. It uses the same set of error messages as perror(3C). The returned string should not be overwritten. The strerror_r() function maps the error number in errnum to anerror message string and returns the string in the buffer pointed to by str- errbuf with length buflen. RETURN VALUES
Upon successful completion, strerror() returns a pointer to the generated message string. Otherwise, it sets errno and returns a pointer to an error message string. It returns the string "Unknown error" if errnum is not a valid error number. Upon successful completion, strerror_r() returns 0. Otherwise it sets errno and returns the value of errno to indicate the error. It returns the string "Unknown error" in the buffer pointed to by strerrbuf if errnum is not a valid error number. ERRORS
These functions may fail if: EINVAL The value of errnum is not a valid error number. The strerror_r() function may fail if: ERANGE The buflen argument specifies insufficient storage to contain the generated message string. USAGE
Messages returned from these functions are in the native language specified by the LC_MESSAGES locale category. See setlocale(3C). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Safe | +-----------------------------+-----------------------------+ SEE ALSO
gettext(3C), perror(3C), setlocale(3C), attributes(5), standards(5) SunOS 5.11 31 Mar 2005 strerror(3C)
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