When defining macros that headers rely on, such as _FILE_OFFSET_BITS, FUSE_USE_VERSION, _GNU_SOURCE among others, where is the best place to put them?
Some possibilities I've considered include
At the top of the any source files that rely on definitions exposed by headers included in that file
Immediately before the include for the relevant header(s)
Define at the CPPFLAGS level via the compiler? (such as -D_FILE_OFFSET_BITS=64) for the:
Entire source repo
The whole project
Just the sources that require it
In project headers, which should also include those relevant headers to which the macros apply
Some other place I haven't thought of, but is infinitely superior
A note: Justification by applicability to make, autotools, and other build systems is a factor in my decision.
If the macros affect system headers, they probably ought to go somewhere where they affect every source file that includes those system headers (which includes those that include them indirectly). The most logical place would therefore be on the command line, assuming your build system allows you to set e.g. CPPFLAGS to affect the compilation of every file.
If you use precompiled headers, and have a precompiled header that must therefore be included first in every source file (e.g. stdafx.h for MSVC projects) then you could put them in there too.
For macros that affect self-contained libraries (whether third-party or written by you), I would create a wrapper header that defines the macros and then includes the library header. All uses of the library from your project should then include your wrapper header rather than including the library header directly. This avoids defining macros unnecessarily, and makes it clear that they relate to that library. If there are dependencies between libraries then you might want to make the macros global (in the build system or precompiled header) just to be on the safe side.
Well, it depends.
Most, I'd define via the command line - in a Makefile or whatever build system you use.
As for _FILE_OFFSET_BITS I really wouldn't define it explicitly, but rather use getconf LFS_CFLAGS and getconf LFS_LDFLAGS.
I would always put them on the command line via CPPFLAGS for the whole project. If you put them any other place, there's a danger that you might forget to copy them into a new source file or include a system header before including the project header that defines them, and this could lead to extremely nasty bugs (like one file declaring a legacy 32-bit struct stat and passing its address to a function in another file which expects a 64-bit struct stat).
BTW, it's really ridiculous that _FILE_OFFSET_BITS=64 still isn't the default on glibc.
Most projects that I've seen use them did it via -D command line options. They are there because that eases building the source with different compilers and system headers. If you were to build with a system compiler for another system that didn't need them or needed a different set of them then a configure script can easily change the command line arguments that a make file passes to the compiler.
It's probably best to do it for the entire program because some of the flags effect which version of a function gets brought in or the size/layout of a struct and mixing those up could cause crazy things if you aren't careful.
They certainly are annoying to keep up with.
For _GNU_SOURCE and the autotools in particular, you could use AC_USE_SYSTEM_EXTENSIONS (citing liberally from the autoconf manual here):
-- Macro: AC_USE_SYSTEM_EXTENSIONS
This macro was introduced in Autoconf 2.60. If possible, enable
extensions to C or Posix on hosts that normally disable the
extensions, typically due to standards-conformance namespace
issues. This should be called before any macros that run the C
compiler. The following preprocessor macros are defined where
appropriate:
_GNU_SOURCE
Enable extensions on GNU/Linux.
__EXTENSIONS__
Enable general extensions on Solaris.
_POSIX_PTHREAD_SEMANTICS
Enable threading extensions on Solaris.
_TANDEM_SOURCE
Enable extensions for the HP NonStop platform.
_ALL_SOURCE
Enable extensions for AIX 3, and for Interix.
_POSIX_SOURCE
Enable Posix functions for Minix.
_POSIX_1_SOURCE
Enable additional Posix functions for Minix.
_MINIX
Identify Minix platform. This particular preprocessor macro
is obsolescent, and may be removed in a future release of
Autoconf.
For _FILE_OFFSET_BITS, you need to call AC_SYS_LARGEFILE and AC_FUNC_FSEEKO:
— Macro: AC_SYS_LARGEFILE
Arrange for 64-bit file offsets, known as large-file support. On some hosts, one must use special compiler options to build programs that can access large files. Append any such options to the output variable CC. Define _FILE_OFFSET_BITS and _LARGE_FILES if necessary.
Large-file support can be disabled by configuring with the --disable-largefile option.
If you use this macro, check that your program works even when off_t is wider than long int, since this is common when large-file support is enabled. For example, it is not correct to print an arbitrary off_t value X with printf("%ld", (long int) X).
The LFS introduced the fseeko and ftello functions to replace their C counterparts fseek and ftell that do not use off_t. Take care to use AC_FUNC_FSEEKO to make their prototypes available when using them and large-file support is enabled.
If you are using autoheader to generate a config.h, you could define the other macros you care about using AC_DEFINE or AC_DEFINE_UNQUOTED:
AC_DEFINE([FUSE_VERSION], [28], [FUSE Version.])
The definition will then get passed to the command line or placed in config.h, if you're using autoheader. The real benefit of AC_DEFINE is that it easily allows preprocessor definitions as a result of configure checks and separates system-specific cruft from the important details.
When writing the .c file, #include "config.h" first, then the interface header (e.g., foo.h for foo.c - this ensures that the header has no missing dependencies), then all other headers.
I usually put them as close as practicable to the things that need them, whilst ensuring you don't set them incorrectly.
Related pieces of information should be kept close to make it easier to identify. A classic example is the ability for C to now allow variable definitions anywhere in the code rather than just at the top of a function:
void something (void) {
// 600 lines of code here
int x = fn(y);
// more code here
}
is a lot better than:
void something (void) {
int x;
// 600 lines of code here
x = fn(y);
// more code here
}
since you don't have to go searching for the type of x in the latter case.
By way of example, if you need to compile a single source file multiple times with different values, you have to do it with the compiler:
gcc -Dmydefine=7 -o binary7 source.c
gcc -Dmydefine=9 -o binary9 source.c
However, if every compilation of that file will use 7, it can be moved closer to the place where it's used:
source.c:
#include <stdio.h>
#define mydefine 7
#include "header_that_uses_mydefine.h"
#define mydefine 7
#include "another_header_that_uses_mydefine.h"
Note that I've done it twice so that it's more localised. This isn't a problem since, if you change only one, the compiler will tell you about it, but it ensures that you know those defines are set for the specific headers.
And, if you're certain that you will never include (for example) bitio.h without first setting BITCOUNT to 8, you can even go so far as to create a bitio8.h file containing nothing but:
#define BITCOUNT 8
#include "bitio.h"
and then just include bitio8.h in your source files.
Global, project-wide constants that are target specific are best put in CCFLAGS in your makefile. Constants you use all over the place can go in appropriate header files which are included by any file that uses them.
For example,
// bool.h - a boolean type for C
#ifndef __BOOL_H__
#define BOOL_H
typedef int bool_t
#define TRUE 1
#define FALSE 0
#endif
Then, in some other header,
`#include "bool.h"`
// blah
Using header files is what I recommend because it allows you to have a code base built by make files and other build systems as well as IDE projects such as Visual Studio. This gives you a single point of definition that can be accompanied by comments (I'm a fan of doxygen which allows you to generate macro documentation).
The other benefit with header files is that you can easily write unit tests to verify that only valid combinations of macros are defined.
Related
I am new to C and am just learning the basics of modularising my code for neatness and maintainability. I am reading a lot of people saying not to include .c files directly but instead to use .h files with associated .c files.
My question is, when writing a library which is exposed/included via its .h file - does the compiler dedupe common includes or are the included each time they are referenced?
For instance in my above application, I am using printf in my main and also in my foo library.
When running:
gcc -o app main foo/foo.c && ./app
I get the expected outputs printed to the console, however does the compiler remove duplicates of the <stdio.h> include or is it included once for main.c and once again for foo.c?
No, the compiler does not remove them. Nor should it, because sometimes (although it's rare) headers are written with the purpose of being included several times with different effects each time. So the compiler can't just omit these subsequent inclusions.
That's why people put include guards in headers (#ifndef FOO_H_ in this case.)
Each file, regardless of whether is a .h or .c file, should include what it needs. It should not rely that a header has already been included somewhere else. If something is included twice in the current compilation unit, the include guards will make sure headers are only included once, regardless of how many files try to include them.
As a side note, #pragma once, even though it's not in the C standard, is a de-facto standard compiler extension. So you can use just do:
#pragma once
void foo();
It's one of those rare cases where a non-standard compiler extension is so widely supported that it's safe to use.
In contrary, each compilation unit ("main.c" and "foo.c" in your case) needs that include. Otherwise the compiler would not know the prototype of printf()(note). Each compilation unit (aka "module") is compiled on its own.
You might mix up headers and linkable files (object code files, and libraries).
The contents of a header file replaces the #include line during preprocessing. "stdio.h" contains only the prototype of printf(), among a lot of other stuff, not the implementation of the function.
If the compiler generates the object code for "main.c" and "foo.c", each of them includes an unresolved reference to printf().
Finally the linker will include the object code for printf(), but just once. This single instance of the function is called by both callers. Here happens what you seem to ask.
You might wonder why you don't have to add the library to your command line. This is a convenience feature of most compiler drivers, as nearly all applications want the standard libraries. You might like to add "-v" to the command line to see what really happens. Other options can suppress this automation.
Note: Some compilers are quite smart and know a lot of standard functions. They will accept the source and produce a nice warning. But don't rely on this.
I got stuck trying to do Exercise 8-3 of K&R, the goal of the exercise is to rewrite some functions of stdio.h such as fopen, fclose, fillbuf and flushbuf
here's how my source files are organized:
stdio.h: contains types and macro definitions, and the declarations of some functions proper to the library. all content of the file is enclosed between #ifndef #endif lines as follows:
#ifndef STDIO_H
#define STDIO_H
/* content of stdio.h */
#endif
myfunction.c: I have a .c file per function, each file has a #include "stdio.h" line to load all needed types definitions.
main.c: where I have code to test my functions, the main.c also has a #include "stdio.h" line.
my problem is the following: when I try to compile all my files using gcc I run to the error:
multiple definition of `_iob'
on every one of my function files where my stdio.h is included, (_iob is a variable I only defined inside my stdio.h)...why is this happening ? I though the #ifndef line was to specifically prevent such errors.
more generally:
How would you go about making your own header files and library/function files and using them in your projects ?
Is there a way to make the linker figure out the position of my functions just by including the header file, the same way it does for standard functions ?
Please become aware of the difference between a library and its header files.
A library is a (collection of) binary machine code (with some additional meta-data, e.g. relocation directives to the linker).
For example, on my Linux system, dynamic libraries are generally shared objects (e.g. /usr/lib/x86_64-linux-gnu/libgmp.so) and it makes absolutely no sense to try some preprocessor directive like #include "libgmp.so" //wrong.
But a library has some API. That API is given by some documentation and by some header file(s), e.g. gmp.h and you should #include "gmp.h" in any C code (your C translation unit) which uses it.
myfunction.c: I have a .c file per function
Having one file per function is often poor taste. You generally can group related functions. For example, in your case, you probably want to define your myfopen and myfclose functions in the same myopenclose.c translation unit (even if you don't have to) because these two functions are intimately related. As a rule of thumb, I prefer having source files of one or a few thousand lines each (but that is really a matter of taste, and some people like having many small files).
Remember that what the compiler really sees is the preprocessed form of code. Consider asking your compiler to produce that form (e.g. from foo.c you can get its preprocessed form foo.i with gcc -C -E -Wall foo.c > foo.i on my Linux desktop) and look into it. Try that on your own files (e.g. your myopenclose.c if you have one).
If you have many small files, the compiler is probably including the same headers in each of them, and these included declarations gets compiled every time. BTW, notice that gcc is only a driver program. Use it with -v flag. You'll see that it is running cc1 (the C compiler proper), as (the assembler), ld (the linker), etc.
I run to the error:
multiple definition of `_iob'
on every one of my function files where my stdio.h is included, (_iob is a variable I only defined inside my stdio.h).
You probably should declare extern your _iob global variable in your stdio.h and define a global _iob in only one implementation file (perhaps myopenclose.c, if it is relevant) of your library.
Don't confuse definition and declaration (of variables, functions, types, etc.). Spend some time reading the C11 standard n1570. These words are defined there. As a rule of thumb, declarations should go into header .h files, definitions (of variables and functions) in implementation .c files (of course details are much more complex, you often but not always define types and struct in header files).
I strongly recommend using some Linux distribution (it is very developer- and student- friendly) and studying the source code of some existing free software C standard library (like musl-libc, whose code is quite readable). More generally, study the source code of existing free software projects (e.g. on github). They will inspire you.
Is there a way to make the linker figure out the position of my functions just by including the header file, the same way it does for standard functions ?
This shows a lot of confusion (the above question does not make any sense). Read more about compilers (your cc1 program -started by gcc- is translating a .c file into some object file .o) and about linkers (your ld, generally started by gcc, is agglomerating several object files, processing relocations inside them, and producing an ELF library or an executable). The preprocessing (e.g. of #include directive) is done at compile time by cc1. The linker cannot see any header files (it only deals with object files or libraries).
If you rewrite some of the system declarations and functions, while at the same time including the system declarations, you can expect some collisions.
Header files (.h) contain code (usually only declarations) and the mechanism you describe (#ifndef STDIO_H) is to prevent multiple inclusions of the same header file - mainly because another include file (header) that has already been loaded might also include it. That result in the same kind of collision as you had.
In C, you could, for instance
make a new header file that contain your own declarations + the stdio ones that don't collide with yours
use the stdio declarations, and only write new functions that use the same structures, defines, enums etc... as stdio
rewrite the necessary declarations and code that allows you not to include the system headers anymore
use another naming convention, like my_iob in both your header file, and in your code.
The two last ones are probably the best in your case, since you still have some collisions coming from a header file.
For instance, your code might not include stdio.h, but another header file you include might do it, indirectly...
So I'm writing portable embedded ansi C code that is attempting to support multiple compilers and hardware targets. Each compiler/hardware vendor has different math.h functions it supports. Some support only C90, some support a subset of C99, others a full set of C99.
I'm trying to find a way to check if a given function exists during preprocessor so that I can use a custom macro if it doesn't exist. Some vendors have extern functions in the math.h, some use #define to remap to some internal call. Is there a piece of code that can tell if it is #defined or an extern function? I can use #ifdef for the define, but what about an actual function call?
The usual solution is instead to look at macros defined by the preprocessor itself, or passed into the build process as -D definitions, which identify the compiler and platform you're running on, and use those plus your knowledge of what special assists each environment needs to configure your code.
I suppose you could write a series of test .c files, try compiling them, look at the error codes coming back, and use those to set appropriate -D flags... but I'm not convinced that would be any cleaner.
I'm working on a 'C' code base that was written specifically for one type of embedded processor. I've written generic 'psuedo object-oriented' code for things like LEDs, GPIO lines and ADCs (using structs, etc). I have also written a large amount of code that utilizes these 'objects' in a hardware/target agnostic manner.
We are now tossing another processor type into the mix, and I'd like to keep the current code structure so I can still make use of the higher level libraries. I do, however, need to provide different implementations for the lower level code (LEDs, GPIO, ADCs).
I know #includes in .C files are generally looked down upon, but in this case, is it appropriate? For example:
// led.c
#ifdef TARGET_AVR
#include "led_avr.c"
#elseifdef TARGET_PIC
#include "led_pic.c"
#else
#error "Unspecified Target"
#endif
If this is inappropriate, what is a better implementation?
Thanks!
Since the linker doesn't care what the name of a source file actually is (it only cares about exported symbols), you can change your linker command line for each target to name the appropriate implementation module (led_avr.c or led_pic.c).
A common way to manage multiple platform source files is to put each set of platform implementation files in their own directory, so you might have avr/led.c and pic/led.c (and avr/gpio.c and pic/gpio.c, etc).
It is good. You may use other tricks, like:
#ifdef PROC1
#define MULTI_CPU(a,b) (a)
#else
#define MULTI_CPU(a,b) (b)
#endif
The more common way to do that, instead of including a C file, is to change the build system (whatever it is) to compile or not compile those certain C files.
I'm trying to streamline large chunk of legacy C code in which, even today, before doing the build guy who maintains it takes a source file(s) and manually modifies the following section before the compilation based on the various types of environment.
The example follows but here's the question. I'm rusty on my C but I do recall that using #ifdef is discouraged. Can you guys offer better alternative? Also - I think some of it (if not all of it) can be set as environment variable or passed in as a parameter and if so - what would be a good way of defining these and then accessing from the source code?
Here's snippet of the code I'm dealing with
#define DAN NO
#define UNIX NO
#define LINUX YES
#define WINDOWS_ES NO
#define WINDOWS_RB NO
/* Later in the code */
#if ((DAN==1) || (UNIX==YES))
#include <sys/param.h>
#endif
#if ((WINDOWS_ES==YES) || (WINDOWS_RB==YES) || (WINDOWS_TIES==YES))
#include <param.h>
#include <io.h>
#include <ctype.h>
#endif
/* And totally insane harcoded paths */
#if (DAN==YES)
char MasterSkipFile[MAXSTR] = "/home/dp120728/tools/testarea/test/MasterSkipFile";
#endif
#if (UNIX==YES)
char MasterSkipFile[MAXSTR] = "/home/tregrp/tre1/tretools/MasterSkipFile";
#endif
#if (LINUX==YES)
char MasterSkipFile[MAXSTR] = "/ptehome/tregrp/tre1/tretools/MasterSkipFile";
#endif
/* So on for every platform and combination */
Sure, you can pass -DWHATEVER on the command line. Or -DWHATEVER_ELSE=NO, etc. Maybe for the paths you could do something like
char MasterSkipFile[MAXSTR] = SOME_COMMAND_LINE_DEFINITION;
and then pass
-DSOME_COMMAND_LINE_DEFINITION="/home/whatever/directory/filename"
on the command line.
One thing we used to do is have a generated .h file with these definitions, and generate it with a script. That helped us get rid of a lot of brittle #ifs and #ifdefs
You need to be careful about what you put there, but machine-specific parameters are good candidates - this is how autoconf/automake work.
EDIT: in your case, an example would be to use the generated .h file to define INCLUDE_SYS_PARAM and INCLUDE_PARAM, and in the code itself use:
#ifdef INCLUDE_SYS_PARAM
#include <sys/param.h>
#endif
#ifdef INCLUDE_PARAM
#include <param.h>
#endif
Makes it much easier to port to new platforms - the existence of a new platform doesn't trickle into the code, only to the generated .h file.
Platform specific configuration headers
I'd have a system to generate the platform-specific configuration into a header that is used in all builds. The AutoConf name is 'config.h'; you can see 'platform.h' or 'porting.h' or 'port.h' or other variations on the theme. This file contains the information needed for the platform being built. You can generate the file by copying a version-controlled platform-specific variant to the standard name. You can use a link instead of copying. Or you can run configuration scripts to determine its contents based on what the script finds on the machine.
Default values for configuration parameters
The code:
#if (DAN==YES)
char MasterSkipFile[MAXSTR] = "/home/dp120728/tools/testarea/MasterSkipFile";
#endif
#if (UNIX==YES)
char MasterSkipFile[MAXSTR] = "/home/tregrp/tre1/tretools/MasterSkipFile";
#endif
#if (LINUX==YES)
char MasterSkipFile[MAXSTR] = "/ptehome/tregrp/tre1/tretools/MasterSkipFile";
#endif
Would be better replaced by:
#ifndef MASTER_SKIP_FILE_PATH
#define MASTER_SKIP_FILE_PATH "/opt/tretools/MasterSkipFile"
#endif
const char MasterSkipFile[] = MASTER_SKIP_FILE_PATH;
Those who want the build in a different location can set the location via:
-DMASTER_SKIP_FILE_PATH='"/ptehome/tregtp/tre1/tretools/PinkElephant"'
Note the use of single and double quotes; try to avoid doing this on the command line with backslashes in the path. You can use a similar default mechanism for all sorts of things:
#ifndef DEFAULTABLE_PARAMETER
#define DEFAULTABLE_PARAMETER default_value
#endif
If you choose your defaults well, this can save a lot of energy.
Relocatable software
I'm not sure about the design of the software that can only be installed in one location. In my book, you need to be able to have the old version 1.12 of the product installed on the machine at the same time as the new 2.1 version, and they should be able to operate independently. A hard-coded path name defeats that.
Parameterize by feature not platform
The key difference between the AutoConf tools and the average alternative system is that the configuration is done based on features, not on platforms. You parameterize your code to identify a feature that you want to use. This is crucial because features tend to appear on platforms other than the original. I look after code where there are lines like:
#if defined(SUN4) || defined(SOLARIS_2) || defined(HP_UX) || \
defined(LINUX) || defined(PYRAMID) || defined(SEQUENT) || \
defined(SEQUENT40) || defined(NCR) ...
#include <sys/types.h>
#endif
It would be much, much better to have:
#ifdef INCLUDE_SYS_TYPES_H
#include <sys/types.h>
#endif
And then on the platforms where it is needed, generate:
#define INCLUDE_SYS_TYPES_H
(Don't take this example header too literally; it is the concept I am trying to get over.)
Treat platform as a bundle of features
As a corollary to the previous point, you do need to detect platform and define the features that are applicable to that platform. This is where you have the platform-specific configuration header which defines the configuration features.
Product features should be enabled in a header
(Elaborating on a comment I made to another answer.)
Suppose you have a bunch of features in the product that need to be included or excluded conditionally. For example:
KVLOCKING
B1SECURITY
C2SECURITY
DYNAMICLOCKS
The relevant code is included when the appropriate define is set:
#ifdef KVLOCKING
...KVLOCKING stuff...
#else
...non-KVLOCKING stuff...
#endif
If you use a source code analysis tool like cscope, then it is helpful if it can show you when KVLOCKING is defined. If the only place where it is defined is in some random Makefiles scattered around the build system (let's assume there are a hundred sub-directories that are used in this), it is hard to tell whether the code is still in use on any of your platforms. If the defines are in a header somewhere - the platform specific header, or maybe a product release header (so version 1.x can have KVLOCKING and version 2.x can include C2SECURITY but 2.5 includes B1SECURITY, etc), then you can see that KVLOCKING code is still in use.
Believe me, after twenty years of development and staff turnover, people don't know whether features are still in use or not (because it is stable and never causes problems - possibly because it is never used). And if the only place to find whether KVLOCKING is still defined is in the Makefiles, then tools like cscope are less helpful - which makes modifying the code more error prone when trying to clean up later.
Its much saner to use :
#if SOMETHING
.. from platform to platform, to avoid confusing broken preprocessors. However any modern compiler should effectively argue your case in the end. If you give more details on your platform, compiler and preprocessor you might receive a more concise answer.
Conditional compilation, given the plethora of operating systems and variants therein is a necessary evil. if, ifdef, etc are most decidedly not an abuse of the preprocessor, just exercising it as intended.
My preferred way would be to have the build system do the OS detection. Complex cases you'd want to isolate the machine-specific stuff into a single source file, and have completely different source files for the different OSes.
So in this case, you'd have a #include "OS_Specific.h" in that file. You put the different includes, and the definition of MasterSkipFile for this platform. You can select between them by specifying different -I (include path directories) on your compiler command line.
The nice thing about doing it this way is that somebody trying to figure out the code (perhaps debugging) doesn't have to wade through (and possibly be misled by) phantom code for a platform they aren't even running on.
I've seen build systems in which most of the source files started something off like this:
#include PLATFORM_CONFIG
#include BUILD_CONFIG
and the compiler was kicked off with:
cc -DPLATFORM_CONFIG="linuxconfig.h" -DBUILD_CONFIG="importonlyconfig.h"
(this may need backslash escapes)
this had the effect of letting you separate out the platform settings in one set of files and the configuration settings in another. Platform settings manages handling library calls that may not exist on one platform or not in the right format as well as defining important size dependent types--things that are platform specific. Build settings handles what features are being enabled in the output.
Generalities
I'm a heretic who has been cast out from the Church of the GNU Autotools. Why? Because I like to understand what the hell my tools are doing. And because I've had the experience of trying to combine two components, each of which insisted on a different, incompatible version of autotools being the default version installed on my computer.
I work by creating one .h file or .c filed for every combination of platform and significant abstraction. I work hard to define a central .h file that says what the interface is. Often this means I wind up creating a "compatibility layer" that insulates me from differences between platforms. Often I wind up using ANSI Standard C whenever possible, instead of platform-specific functionality.
I sometimes write scripts to generate platform-dependent files. But the scripts are always written by hand and documented, so I know what they do.
I admire Glenn Fowler's nmake and Phong Vo's iffe (if feature exists), which I think are better engineered than the GNU tools. But these tools are part of the AT&T Software Technology suite, and I haven't been able to figure out how to use them without buying into the whole AST way of doing things, which I don't always understand.
Your example
There clearly needs to be
extern char MasterSkipFile[];
in a .h file somewhere, and you can then link against a suitable .o.
The conditional inclusion of the "right set of .h files for the platform" is something I would handle by trying to stick to ANSI C when possible, and when not possible, defining a compatibility layer in a platform-specific .h file. As it is, I can't tell what names the #includes are trying to import, so I can't give more specific advice.