I'm using tempnam() only to get the directory name, so this security warning does not apply to my case. How can I disable it? I couldn't find any switches to do it.
If you really only want the directory name, use the string constant macro P_tmpdir, defined in <stdio.h>.
"The tempnam() function returns a pointer to a string that is a valid filename, and such that a file with this name did not exist when tempnam() checked."
The warning arises because of the race condition between checking and a later creating of the file.
You want to only get the directory name? What should that be good for?
Like stranger already said, you may disable this (and similar warnings) using -Wno-deprecated-declarations.
The answer is no, because - on many systems - the GNU C library (glibc) which implements this function is compiled so as to trigger a linker warnings when it is used.
See:
GCC bug page regarding this issue - I filed this a short while ago.
GNU ld bug page regarding this issue - filed in 2010!
GNU ld bug page suggesting an approach for resolving the issue - I filed this a short while ago.
Note that the problem is not specific to GCC - any linker is supposed to emit this warning, its trigger is "hard-coded" in the compiled library.
If you want to create a temporary directory that's unique for the process, you can use mkdtemp.
This can, e.g., be useful to create FIFOs in there, or when a program needs to create lots of temporary files or trees of directories and files: Then they can be put into that directory.
As linker warning it may be obfuscated by using this answer's ASM workaround/hack:
https://stackoverflow.com/a/29205123/2550395
Something like this (quick and dirty):
#include <stdio.h>
#include <fcntl.h>
#include <sys/stat.h>
char my_file[20];
#define __hide_section_warning(section_string) \
__asm__ (".section " section_string "\n.string \"\rquidquid agis prudenter agas et respice finem \"\n\t.previous");
/* If you want to hide the linker's output */
#define hide_warning(symbol) \
__hide_section_warning (".gnu.warning." #symbol)
hide_warning(tmpnam)
tmpnam( my_file );
lock_fd = open( my_file, O_CREAT | O_WRONLY, (S_IRUSR | S_IWUSR | S_IRGRP) );
However, it still will leave a trace in the Make.p file and therefore isn't perfectly clean, besides already being a hack.
PS: It works on my machine ¯\_(ツ)_/¯
You can use GCC's -Wno-deprecated-declarations option to disable all warnings like this. I suggest you handle the warning properly, though, and take the suggestion of the compiler.
Related
I currently invoke clang or gcc as
cc -E -DPREPROCESSING ...
when debugging macros.
It has occurred to me that the define is redundant. Is there an expression I could write in the source to detect when the compiler will stop after preprocessing, and so drop this definition from my build scripts?
#if magic
#define PREPROCESSING
#ending
A look at the docs suggests not, but with luck I'm missing something.
Whatever solution you come up with is going to be compiler-specific, since the C standard does not have anything to say about separate preprocessing.
In gcc, you could implement the magic by adding a custom spec file:
%rename cpp old_cpp
*cpp:
%{E:-DPREPROCESSING} %(old_cpp)
You would need to tell gcc to use this spec file (-specs=/path/to/specfile), unless you compiled your own gcc with the above definition added to the built-in cpp spec. If you are using a Makefile, you could add the -specs option above to your CFLAGS.
(I should add that I don't think this is a particularly good idea. But it is possible.)
I'm writing library routines of which some characteristics can be tailored through #include'ing a configuration file. However, I'd like this configuration file to be optional, some default parameters being provided in the source. Here is a typical source beginning:
#include "userconf.h"
#ifndef BUFSIZE
#define BUFSIZE 100
#endif
...
where file userconf.h, if it exists, contains:
#define BUFSIZE 255
Standard compilers (gcc or others) consider a missing #include file an error (and they're right!). In this case, and only for this line, I'd like the compiler to continue without objection since default values are provided for parameters expected from the missing configuration file.
Is there a way to do this?
Note: I don't mind checking for this existence of the file from the make system (I'm using CMake) and passing a -Doption if that's easier to do (but, please, provide CMake directives for it, I'm not familiar with it and open documentation gives a hard time to grab the whole picture).
I found the answer "by accident" when including the wrong file.
You make profit of the multiple include directory search feature of the compiler (aka. -I option). You arrange your -I option list in such a way that there is a directory, preferentially at the end of the chain, containing a skeletal version of the configuration file.
For example, directory default/ contains the following userconf.h:
#define BUFSIZE 255
and the developement directory develop/ contains the live userconf.h:
#define BUFSIZE 100
Then, the source file of the original question may be compiled with
gcc source.c -Idevelop -Idefault ...
and -Idevelop may be omitted if it is part of the default searched directories.
i'm using cs50 appliance.
i've tried to write a new file test.c , found as long as i include int i line, it doesn't generate a new file test, if i remove that line and make again, it can generate test file. then i made changes on the test file, it still output the original file result, no reflect the new changes.
#include <stdio.h>
#include <cs50.h>
int
main (void)
{
printf("Number: \n");
int i = GetInt();
}
it was running properly before though... anyone can help please?
Apparently your default rules for make run the compiler on test.c.
The compiler notices that you are assigning a value to variable i, but you never use that value in any way; it would normally report this as a warning.
Apparently either your compiler or make are configured in such a way that this warning becomes a fatal error to make.
The remedy is to use the variable. It looks as though you need to pick up a book on the C programming language, or follow a course, if that's not what you're doing already.
I have some C source files that need to be pre-processed so that I can use another application to add Code Coverage instrumentation code in my file.
To do so, I use GCC (I'm using this on a LEON2 processor so it's a bit modified but it's essentially GCC 3.4.4) with the following command line:
sparc-elf-gcc -DUNIT_TEST -I. ../Tested_Code/0_BSW/PKG_CMD/MEMORY.c -E > MEMORY.i
With a standard file this works perfectly, but this one the programmer used a #ifndef UNIT_TEST close and no matter what I do the code won't be pre-processed. I don't understand why since I'm passing -DUNIT_TEST to GCC explicitly defining it.
Does anyone have any clue what could cause this? I checked the resulting .i file and as expected my UNIT_TEST code is not present in it so I get an error when instrumenting it.
Anything wrapped in an #ifndef will only be parsed if it's NOT defined so you need to remove that definition to get all the code that is inside that block. GCC can't spit out preprocessed info for all the #ifdef and #ifndef if at preprocessing times symbols are/aren't defined.
How do I at compile time undefine a compiler macro using gcc. I tried some compile args to gcc like -D but I can't get to see the "not defined" message.
Thanks
#include <iostream>
#define MYDEF
int main(){
#ifdef MYDEF
std::cout<<"defined\n";
#else
std::cout<<"not defined\n";
#endif
}
You can use the -U option with gcc, but it won't undefine a macro defined in your source code. As far as I know, there's no way to do that.
You should wrap the MYDEF definition in a preprocessor macro, the presence of which (defined on the command line) would then prevent MYDEF from being defined. A bit convoluted to be sure but you can then control the build in the way you want from the command line (or Makefile). Example:
#ifndef DONT_DEFINE_MYDEF
#define MYDEF
#endif
Then from the command line when you don't want MYDEF:
gcc -DDONT_DEFINE_MYDEF ...
http://gcc.gnu.org/onlinedocs/gcc-4.4.2/gcc/Preprocessor-Options.html#Preprocessor-Options
The -U options seemed like what you could have needed... but then again you can't override a definition contained in your source code without resorting to more preprocessor directives.
You can resort to filtering source code and give this back to gcc for compilation, like this pseudo code:
grep -v "define MYDEF" yourFile.c | gcc -o yourFile.o -xc -
Hope it helps.
The code use case is not right. As I see, you have hard coded #define in the file. If compiler initially assumes MYDEF undefined, it will define it once it start processing the file.
You should remove the line #define MYDEF. And I hope your test case will work, if you pass MYDEF to -D and -U.
Here is one possibility that doesn't completely cover your use case but which I found to be helpful in my case.
If your MYDEF were #defined in a separate header file #included from the .c file you could force the definition of the #include guard macro with the -D option (thus preventing the MYDEF #definition) then either actively #define (still with the -D option) MYDEF to something else or just leave it undefined.
It is clear that anything else defined in the header file would also be missing but this was for me a solution to forcedly undefine a macro without changing the third-party code.