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authorRical Jasan <ricaljasan@pacific.net>2015-03-06 00:59:49 -0500
committerMike Frysinger <vapier@gentoo.org>2015-03-06 00:59:49 -0500
commit7e7af3496ee4b13366726546dd8b712a698fa5c4 (patch)
treeaed8bc5f9a31d2246c079b00e461310090d38d20 /manual
parent4ca8ddfb05ea7d888347bb96cfa431e0eb7fcd9a (diff)
manual: complete example in error message documentation
The manual gives "an example showing how to handle failure to open a file correctly." The example function, open_sesame, uses the newly-introduced strerror function and errno and program_invocation_short_name variables. It fails to specify GNU extensions, however, so attempts to use it in the following way: int main (void) {open_sesame ("badname");} fail during compilation with "error: ‘program_invocation_short_name’ undeclared", indicating the example is incomplete. The presence of "#include"s suggest everything neccesary for the function to work should be present. For completeness, the example is lacking the following line: #define _GNU_SOURCE as the declarations of program_invocation_*name in errno.h are wrapped in an "#ifdef __USE_GNU" conditional. The documentation of the variables is also expanded, adding that their definition lies in errno.h and noting specifically they are GNU extensions.
Diffstat (limited to 'manual')
-rw-r--r--manual/errno.texi18
1 files changed, 12 insertions, 6 deletions
diff --git a/manual/errno.texi b/manual/errno.texi
index 315320dfa8..1068be3a50 100644
--- a/manual/errno.texi
+++ b/manual/errno.texi
@@ -1377,6 +1377,8 @@ This variable's value is the name that was used to invoke the program
running in the current process. It is the same as @code{argv[0]}. Note
that this is not necessarily a useful file name; often it contains no
directory names. @xref{Program Arguments}.
+
+This variable is a GNU extension and is declared in @file{errno.h}.
@end deftypevar
@comment errno.h
@@ -1386,17 +1388,19 @@ This variable's value is the name that was used to invoke the program
running in the current process, with directory names removed. (That is
to say, it is the same as @code{program_invocation_name} minus
everything up to the last slash, if any.)
+
+This variable is a GNU extension and is declared in @file{errno.h}.
@end deftypevar
The library initialization code sets up both of these variables before
calling @code{main}.
-@strong{Portability Note:} These two variables are GNU extensions. If
-you want your program to work with non-GNU libraries, you must save the
-value of @code{argv[0]} in @code{main}, and then strip off the directory
-names yourself. We added these extensions to make it possible to write
-self-contained error-reporting subroutines that require no explicit
-cooperation from @code{main}.
+@strong{Portability Note:} If you want your program to work with
+non-GNU libraries, you must save the value of @code{argv[0]} in
+@code{main}, and then strip off the directory names yourself. We
+added these extensions to make it possible to write self-contained
+error-reporting subroutines that require no explicit cooperation from
+@code{main}.
Here is an example showing how to handle failure to open a file
correctly. The function @code{open_sesame} tries to open the named file
@@ -1410,6 +1414,8 @@ save it in a local variable instead, because those other library
functions might overwrite @code{errno} in the meantime.
@smallexample
+#define _GNU_SOURCE
+
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>