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authorRoland McGrath <roland@gnu.org>1996-06-07 20:37:41 +0000
committerRoland McGrath <roland@gnu.org>1996-06-07 20:37:41 +0000
commit9f447fb32c8f4944ef0c5c677be44e17b3fc529b (patch)
treef8237c308b683c96697629122c0a5531fa6c8c1f /manual/lang.texi
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Fri Jun 7 09:11:17 1996 Roland McGrath <roland@delasyd.gnu.ai.mit.edu>
* mach/mach_syscalls.c: Obsolete file removed. * mach/mach_syscalls.h: Likewise. * mach/mach_traps.S: Likewise. * mach/msg_destroy.c: Likewise. * mach/vm_page_size.c: Likewise.
Diffstat (limited to 'manual/lang.texi')
-rw-r--r--manual/lang.texi77
1 files changed, 56 insertions, 21 deletions
diff --git a/manual/lang.texi b/manual/lang.texi
index 66d41846d2..18a1da3b22 100644
--- a/manual/lang.texi
+++ b/manual/lang.texi
@@ -11,7 +11,7 @@ features has been written, we are publishing it here.
* Consistency Checking:: Using @code{assert} to abort if
something ``impossible'' happens.
* Variadic Functions:: Defining functions with varying numbers
- of args.
+ of args.
* Null Pointer Constant:: The macro @code{NULL}.
* Important Data Types:: Data types for object sizes.
* Data Type Measurements:: Parameters of data type representations.
@@ -25,8 +25,8 @@ features has been written, we are publishing it here.
When you're writing a program, it's often a good idea to put in checks
at strategic places for ``impossible'' errors or violations of basic
-assumptions. These checks are helpful in debugging problems due to
-misunderstandings between different parts of the program.
+assumptions. These kinds of checks are helpful in debugging problems
+with the interfaces between different parts of the program, for example.
@pindex assert.h
The @code{assert} macro, defined in the header file @file{assert.h},
@@ -57,16 +57,19 @@ program (@pxref{Aborting a Program}) after printing a message of the
form:
@smallexample
-@file{@var{file}}:@var{linenum}: Assertion `@var{expression}' failed.
+@file{@var{file}}:@var{linenum}: @var{function}: Assertion `@var{expression}' failed.
@end smallexample
@noindent
on the standard error stream @code{stderr} (@pxref{Standard Streams}).
The filename and line number are taken from the C preprocessor macros
@code{__FILE__} and @code{__LINE__} and specify where the call to
-@code{assert} was written.
+@code{assert} was written. When using the GNU C compiler, the name of
+the function which calls @code{assert} is taken from the built-in
+variable @code{__PRETTY_FUNCTION__}; with older compilers, the function
+name and following colon are omitted.
-If the preprocessor macro @code{NDEBUG} is defined at the point where
+If the preprocessor macro @code{NDEBUG} is defined before
@file{assert.h} is included, the @code{assert} macro is defined to do
absolutely nothing.
@@ -77,6 +80,38 @@ with arguments that involve side effects. For example, @code{assert
@code{NDEBUG} is defined.
@end deftypefn
+Sometimes the ``impossible'' condition you want to check for is an error
+return from an operating system function. Then it is useful to display
+not only where the program crashes, but also what error was returned.
+The @code{assert_perror} macro makes this easy.
+
+@comment assert.h
+@comment GNU
+@deftypefn Macro void assert_perror (int @var{errnum})
+Similar to @code{assert}, but verifies that @var{errnum} is zero.
+
+If @code{NDEBUG} is defined, @code{assert_perror} tests the value of
+@var{errnum}. If it is nonzero, @code{assert_perror} aborts the program
+after a printing a message of the form:
+
+@smallexample
+@file{@var{file}}:@var{linenum}: @var{function}: @var{error text}
+@end smallexample
+
+@noindent
+on the standard error stream. The file name, line number, and function
+name are as for @code{assert}. The error text is the result of
+@w{@code{strerror (@var{errnum})}}. @xref{Error Messages}.
+
+Like @code{assert}, if @code{NDEBUG} is defined before @file{assert.h}
+is included, the @code{assert_perror} macro does absolutely nothing. It
+does not evaluate the argument, so @var{errnum} should not have any side
+effects. It is best for @var{errnum} to be a just simple variable
+reference; often it will be @code{errno}.
+
+This macro is a GNU extension.
+@end deftypefn
+
@strong{Usage note:} The @code{assert} facility is designed for
detecting @emph{internal inconsistency}; it is not suitable for
reporting invalid input or improper usage by @emph{the user} of the
@@ -86,8 +121,8 @@ The information in the diagnostic messages printed by the @code{assert}
macro is intended to help you, the programmer, track down the cause of a
bug, but is not really useful for telling a user of your program why his
or her input was invalid or why a command could not be carried out. So
-you can't use @code{assert} to print the error messages for these
-eventualities.
+you can't use @code{assert} or @code{assert_perror} to print the error
+messages for these eventualities.
What's more, your program should not abort when given invalid input, as
@code{assert} would do---it should exit with nonzero status (@pxref{Exit
@@ -120,7 +155,7 @@ of arguments, using @file{varargs.h}.
@menu
* Why Variadic:: Reasons for making functions take
- variable arguments.
+ variable arguments.
* How Variadic:: How to define and call variadic functions.
* Variadic Example:: A complete example.
@end menu
@@ -189,7 +224,7 @@ additional variable arguments. @xref{Calling Variadics}.
with variable arguments.
* Receiving Arguments:: Steps you must follow to access the
optional argument values.
-* How Many Arguments:: How to decide whether there are more arguments.
+* How Many Arguments:: How to decide whether there are more arguments.
* Calling Variadics:: Things you need to know about calling
variable arguments functions.
* Argument Macros:: Detailed specification of the macros
@@ -205,16 +240,16 @@ additional variable arguments. @xref{Calling Variadics}.
A function that accepts a variable number of arguments must be declared
with a prototype that says so. You write the fixed arguments as usual,
-and then tack on @samp{@dots{}} to indicate the possibility of
+and then tack on @samp{@dots{}} to indicate the possibility of
additional arguments. The syntax of ANSI C requires at least one fixed
argument before the @samp{@dots{}}. For example,
@smallexample
-int
+int
func (const char *a, int b, @dots{})
@{
@dots{}
-@}
+@}
@end smallexample
@noindent
@@ -271,7 +306,7 @@ compiler. But you might as well call @code{va_end} just in case your
program is someday compiled with a peculiar compiler.)
@end enumerate
-@xref{Argument Macros}, for the full definitions of @code{va_start},
+@xref{Argument Macros}, for the full definitions of @code{va_start},
@code{va_arg} and @code{va_end}.
Steps 1 and 3 must be performed in the function that accepts the
@@ -405,7 +440,7 @@ found in the header file @file{varargs.h}.
@deftypefn {Macro} @var{type} va_arg (va_list @var{ap}, @var{type})
The @code{va_arg} macro returns the value of the next optional argument,
and modifies the value of @var{ap} to point to the subsequent argument.
-Thus, successive uses of @code{va_arg} return successive optional
+Thus, successive uses of @code{va_arg} return successive optional
arguments.
The type of the value returned by @code{va_arg} is @var{type} as
@@ -478,7 +513,7 @@ functions:
@comment Unix
@deffn Macro va_alist
This macro stands for the argument name list required in a variadic
-function.
+function.
@end deffn
@comment varargs.h
@@ -537,7 +572,7 @@ The result of subtracting two pointers in C is always an integer, but the
precise data type varies from C compiler to C compiler. Likewise, the
data type of the result of @code{sizeof} also varies between compilers.
ANSI defines standard aliases for these two types, so you can refer to
-them in a portable fashion. They are defined in the header file
+them in a portable fashion. They are defined in the header file
@file{stddef.h}.
@pindex stddef.h
@@ -601,7 +636,7 @@ which give you this information in full detail.
* Width of Type:: How many bits does an integer type hold?
* Range of Type:: What are the largest and smallest values
that an integer type can hold?
-* Floating Type Macros:: Parameters that measure the floating point types.
+* Floating Type Macros:: Parameters that measure the floating point types.
* Structure Measurement:: Getting measurements on structure types.
@end menu
@@ -814,7 +849,7 @@ machine.
* Floating Point Concepts:: Definitions of terminology.
* Floating Point Parameters:: Details of specific macros.
* IEEE Floating Point:: The measurements for one common
- representation.
+ representation.
@end menu
@node Floating Point Concepts
@@ -865,7 +900,7 @@ follows.
The @dfn{mantissa} or @dfn{significand}, an unsigned integer which is a
part of each floating point number.
-@item
+@item
@cindex precision (of floating point number)
The @dfn{precision} of the mantissa. If the base of the representation
is @var{b}, then the precision is the number of base-@var{b} digits in
@@ -1149,7 +1184,7 @@ supposed to be greater than @code{1E-9}.
@node IEEE Floating Point
@subsubsection IEEE Floating Point
-@cindex IEEE floating point representation
+@cindex IEEE floating point representation
@cindex floating point, IEEE
Here is an example showing how the floating type measurements come out