I'm working with IRAF, based on SPP, kind of a mix between Fortran and C. I'm looking for a way of referring to a string content when using ls. For example, I can type ls *hola* if I want to list every file containing the word hola in my directory. Supose I have an string called id whose content is the world hola. How could I refer to the content in id? I'm looking for some sort of ls id (I know that construction won't work) which returns the same result as in ls *hola*.
Thank you in advance.
EDIT: SPP is somehow hidden on the Internet but here you have a reference manual https://www.mn.uio.no/astro/english/services/it/help/visualization/iraf/SPPManual.pdf although I haven't found any information there related to this topic.
Using the C side of your SPP thing, if you have access to the C headers, the simple is use something like
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char* command = "ls";
char* args = "*.c";
char line[80];
sprintf( line, " %s %s\n", command, args );
system(line);
};
But in C you have dirent.h where you can find the functions that does this things. Try man opendir on your machine
OPENDIR(3) Linux Programmer's Manual OPENDIR(3)
NAME
opendir, fdopendir - open a directory
SYNOPSIS
#include <sys/types.h>
#include <dirent.h>
DIR *opendir(const char *name);
DIR *fdopendir(int fd);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
fdopendir():
Since glibc 2.10:
_POSIX_C_SOURCE >= 200809L
Before glibc 2.10:
_GNU_SOURCE
DESCRIPTION
The opendir() function opens a directory stream corresponding to the directory name, and returns a pointer to
the directory stream. The stream is positioned at the first entry in the directory.
The fdopendir() function is like opendir(), but returns a directory stream for the directory referred to by
the open file descriptor fd. After a successful call to fdopendir(), fd is used internally by the implementa‐
tion, and should not otherwise be used by the application.
RETURN VALUE
...
First, I would recommend not to use SPP (and IRAF) at all. IRAF is out of official maintainance now, and writing new code for a deprecated software is probably a dead end.
Concerning your question: SPP comes with a function fntopnb() for IRAF style access to filename templates. They are documented at pages 101ff. of the SPP manual. A usage example can be found in the sources of pkg/system/files.x of IRAF:
call salloc (fname, SZ_FNAME, TY_CHAR)
list = fntopnb ("*id*", NO)
while (fntgfnb (list, Memc[fname], SZ_FNAME) != EOF) {
call printf ("%s\n")
call pargstr (Memc[fname])
}
call fntclsb (list)
Is there a platform-agnostic and filesystem-agnostic method to obtain the full path of the directory from where a program is running using C/C++? Not to be confused with the current working directory. (Please don't suggest libraries unless they're standard ones like clib or STL.)
(If there's no platform/filesystem-agnostic method, suggestions that work in Windows and Linux for specific filesystems are welcome too.)
Here's code to get the full path to the executing app:
Variable declarations:
char pBuf[256];
size_t len = sizeof(pBuf);
Windows:
int bytes = GetModuleFileName(NULL, pBuf, len);
return bytes ? bytes : -1;
Linux:
int bytes = MIN(readlink("/proc/self/exe", pBuf, len), len - 1);
if(bytes >= 0)
pBuf[bytes] = '\0';
return bytes;
If you fetch the current directory when your program first starts, then you effectively have the directory your program was started from. Store the value in a variable and refer to it later in your program. This is distinct from the directory that holds the current executable program file. It isn't necessarily the same directory; if someone runs the program from a command prompt, then the program is being run from the command prompt's current working directory even though the program file lives elsewhere.
getcwd is a POSIX function and supported out of the box by all POSIX compliant platforms. You would not have to do anything special (apart from incliding the right headers unistd.h on Unix and direct.h on windows).
Since you are creating a C program it will link with the default c run time library which is linked to by ALL processes in the system (specially crafted exceptions avoided) and it will include this function by default. The CRT is never considered an external library because that provides the basic standard compliant interface to the OS.
On windows getcwd function has been deprecated in favour of _getcwd. I think you could use it in this fashion.
#include <stdio.h> /* defines FILENAME_MAX */
#ifdef WINDOWS
#include <direct.h>
#define GetCurrentDir _getcwd
#else
#include <unistd.h>
#define GetCurrentDir getcwd
#endif
char cCurrentPath[FILENAME_MAX];
if (!GetCurrentDir(cCurrentPath, sizeof(cCurrentPath)))
{
return errno;
}
cCurrentPath[sizeof(cCurrentPath) - 1] = '\0'; /* not really required */
printf ("The current working directory is %s", cCurrentPath);
This is from the cplusplus forum
On windows:
#include <string>
#include <windows.h>
std::string getexepath()
{
char result[ MAX_PATH ];
return std::string( result, GetModuleFileName( NULL, result, MAX_PATH ) );
}
On Linux:
#include <string>
#include <limits.h>
#include <unistd.h>
std::string getexepath()
{
char result[ PATH_MAX ];
ssize_t count = readlink( "/proc/self/exe", result, PATH_MAX );
return std::string( result, (count > 0) ? count : 0 );
}
On HP-UX:
#include <string>
#include <limits.h>
#define _PSTAT64
#include <sys/pstat.h>
#include <sys/types.h>
#include <unistd.h>
std::string getexepath()
{
char result[ PATH_MAX ];
struct pst_status ps;
if (pstat_getproc( &ps, sizeof( ps ), 0, getpid() ) < 0)
return std::string();
if (pstat_getpathname( result, PATH_MAX, &ps.pst_fid_text ) < 0)
return std::string();
return std::string( result );
}
If you want a standard way without libraries: No. The whole concept of a directory is not included in the standard.
If you agree that some (portable) dependency on a near-standard lib is okay: Use Boost's filesystem library and ask for the initial_path().
IMHO that's as close as you can get, with good karma (Boost is a well-established high quality set of libraries)
I know it is very late at the day to throw an answer at this one but I found that none of the answers were as useful to me as my own solution. A very simple way to get the path from your CWD to your bin folder is like this:
int main(int argc, char* argv[])
{
std::string argv_str(argv[0]);
std::string base = argv_str.substr(0, argv_str.find_last_of("/"));
}
You can now just use this as a base for your relative path. So for example I have this directory structure:
main
----> test
----> src
----> bin
and I want to compile my source code to bin and write a log to test I can just add this line to my code.
std::string pathToWrite = base + "/../test/test.log";
I have tried this approach on Linux using full path, alias etc. and it works just fine.
NOTE:
If you are on windows you should use a '\' as the file separator not '/'. You will have to escape this too for example:
std::string base = argv[0].substr(0, argv[0].find_last_of("\\"));
I think this should work but haven't tested, so comment would be appreciated if it works or a fix if not.
Filesystem TS is now a standard ( and supported by gcc 5.3+ and clang 3.9+ ), so you can use current_path() function from it:
std::string path = std::experimental::filesystem::current_path();
In gcc (5.3+) to include Filesystem you need to use:
#include <experimental/filesystem>
and link your code with -lstdc++fs flag.
If you want to use Filesystem with Microsoft Visual Studio, then read this.
No, there's no standard way. I believe that the C/C++ standards don't even consider the existence of directories (or other file system organizations).
On Windows the GetModuleFileName() will return the full path to the executable file of the current process when the hModule parameter is set to NULL. I can't help with Linux.
Also you should clarify whether you want the current directory or the directory that the program image/executable resides. As it stands your question is a little ambiguous on this point.
On Windows the simplest way is to use the _get_pgmptr function in stdlib.h to get a pointer to a string which represents the absolute path to the executable, including the executables name.
char* path;
_get_pgmptr(&path);
printf(path); // Example output: C:/Projects/Hello/World.exe
Maybe concatenate the current working directory with argv[0]? I'm not sure if that would work in Windows but it works in linux.
For example:
#include <stdio.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char **argv) {
char the_path[256];
getcwd(the_path, 255);
strcat(the_path, "/");
strcat(the_path, argv[0]);
printf("%s\n", the_path);
return 0;
}
When run, it outputs:
jeremy#jeremy-desktop:~/Desktop$ ./test
/home/jeremy/Desktop/./test
For Win32 GetCurrentDirectory should do the trick.
You can not use argv[0] for that purpose, usually it does contain full path to the executable, but not nessesarily - process could be created with arbitrary value in the field.
Also mind you, the current directory and the directory with the executable are two different things, so getcwd() won't help you either.
On Windows use GetModuleFileName(), on Linux read /dev/proc/procID/.. files.
Just my two cents, but doesn't the following code portably work in C++17?
#include <iostream>
#include <filesystem>
namespace fs = std::filesystem;
int main(int argc, char* argv[])
{
std::cout << "Path is " << fs::path(argv[0]).parent_path() << '\n';
}
Seems to work for me on Linux at least.
Based on the previous idea, I now have:
std::filesystem::path prepend_exe_path(const std::string& filename, const std::string& exe_path = "");
With implementation:
fs::path prepend_exe_path(const std::string& filename, const std::string& exe_path)
{
static auto exe_parent_path = fs::path(exe_path).parent_path();
return exe_parent_path / filename;
}
And initialization trick in main():
(void) prepend_exe_path("", argv[0]);
Thanks #Sam Redway for the argv[0] idea. And of course, I understand that C++17 was not around for many years when the OP asked the question.
Just to belatedly pile on here,...
there is no standard solution, because the languages are agnostic of underlying file systems, so as others have said, the concept of a directory based file system is outside the scope of the c / c++ languages.
on top of that, you want not the current working directory, but the directory the program is running in, which must take into account how the program got to where it is - ie was it spawned as a new process via a fork, etc. To get the directory a program is running in, as the solutions have demonstrated, requires that you get that information from the process control structures of the operating system in question, which is the only authority on this question. Thus, by definition, its an OS specific solution.
#include <windows.h>
using namespace std;
// The directory path returned by native GetCurrentDirectory() no end backslash
string getCurrentDirectoryOnWindows()
{
const unsigned long maxDir = 260;
char currentDir[maxDir];
GetCurrentDirectory(maxDir, currentDir);
return string(currentDir);
}
For Windows system at console you can use system(dir) command. And console gives you information about directory and etc. Read about the dir command at cmd. But for Unix-like systems, I don't know... If this command is run, read bash command. ls does not display directory...
Example:
int main()
{
system("dir");
system("pause"); //this wait for Enter-key-press;
return 0;
}
Works with starting from C++11, using experimental filesystem, and C++14-C++17 as well using official filesystem.
application.h:
#pragma once
//
// https://en.cppreference.com/w/User:D41D8CD98F/feature_testing_macros
//
#ifdef __cpp_lib_filesystem
#include <filesystem>
#else
#include <experimental/filesystem>
namespace std {
namespace filesystem = experimental::filesystem;
}
#endif
std::filesystem::path getexepath();
application.cpp:
#include "application.h"
#ifdef _WIN32
#include <windows.h> //GetModuleFileNameW
#else
#include <limits.h>
#include <unistd.h> //readlink
#endif
std::filesystem::path getexepath()
{
#ifdef _WIN32
wchar_t path[MAX_PATH] = { 0 };
GetModuleFileNameW(NULL, path, MAX_PATH);
return path;
#else
char result[PATH_MAX];
ssize_t count = readlink("/proc/self/exe", result, PATH_MAX);
return std::string(result, (count > 0) ? count : 0);
#endif
}
For relative paths, here's what I did. I am aware of the age of this question, I simply want to contribute a simpler answer that works in the majority of cases:
Say you have a path like this:
"path/to/file/folder"
For some reason, Linux-built executables made in eclipse work fine with this. However, windows gets very confused if given a path like this to work with!
As stated above there are several ways to get the current path to the executable, but the easiest way I find works a charm in the majority of cases is appending this to the FRONT of your path:
"./path/to/file/folder"
Just adding "./" should get you sorted! :) Then you can start loading from whatever directory you wish, so long as it is with the executable itself.
EDIT: This won't work if you try to launch the executable from code::blocks if that's the development environment being used, as for some reason, code::blocks doesn't load stuff right... :D
EDIT2: Some new things I have found is that if you specify a static path like this one in your code (Assuming Example.data is something you need to load):
"resources/Example.data"
If you then launch your app from the actual directory (or in Windows, you make a shortcut, and set the working dir to your app dir) then it will work like that.
Keep this in mind when debugging issues related to missing resource/file paths. (Especially in IDEs that set the wrong working dir when launching a build exe from the IDE)
A library solution (although I know this was not asked for).
If you happen to use Qt:
QCoreApplication::applicationDirPath()
Path to the current .exe
#include <Windows.h>
std::wstring getexepathW()
{
wchar_t result[MAX_PATH];
return std::wstring(result, GetModuleFileNameW(NULL, result, MAX_PATH));
}
std::wcout << getexepathW() << std::endl;
// -------- OR --------
std::string getexepathA()
{
char result[MAX_PATH];
return std::string(result, GetModuleFileNameA(NULL, result, MAX_PATH));
}
std::cout << getexepathA() << std::endl;
On POSIX platforms, you can use getcwd().
On Windows, you may use _getcwd(), as use of getcwd() has been deprecated.
For standard libraries, if Boost were standard enough for you, I would have suggested Boost::filesystem, but they seem to have removed path normalization from the proposal. You may have to wait until TR2 becomes readily available for a fully standard solution.
Boost Filesystem's initial_path() behaves like POSIX's getcwd(), and neither does what you want by itself, but appending argv[0] to either of them should do it.
You may note that the result is not always pretty--you may get things like /foo/bar/../../baz/a.out or /foo/bar//baz/a.out, but I believe that it always results in a valid path which names the executable (note that consecutive slashes in a path are collapsed to one).
I previously wrote a solution using envp (the third argument to main() which worked on Linux but didn't seem workable on Windows, so I'm essentially recommending the same solution as someone else did previously, but with the additional explanation of why it is actually correct even if the results are not pretty.
As Minok mentioned, there is no such functionality specified ini C standard or C++ standard. This is considered to be purely OS-specific feature and it is specified in POSIX standard, for example.
Thorsten79 has given good suggestion, it is Boost.Filesystem library. However, it may be inconvenient in case you don't want to have any link-time dependencies in binary form for your program.
A good alternative I would recommend is collection of 100% headers-only STLSoft C++ Libraries Matthew Wilson (author of must-read books about C++). There is portable facade PlatformSTL gives access to system-specific API: WinSTL for Windows and UnixSTL on Unix, so it is portable solution. All the system-specific elements are specified with use of traits and policies, so it is extensible framework. There is filesystem library provided, of course.
The linux bash command
which progname will report a path to program.
Even if one could issue the which command from within your program and direct the output to a tmp file and the program
subsequently reads that tmp file, it will not tell you if that program is the one executing. It only tells you where a program having that name is located.
What is required is to obtain your process id number, and to parse out the path to the name
In my program I want to know if the program was
executed from the user's bin directory or from another in the path
or from /usr/bin. /usr/bin would contain the supported version.
My feeling is that in Linux there is the one solution that is portable.
Use realpath() in stdlib.h like this:
char *working_dir_path = realpath(".", NULL);
The following worked well for me on macOS 10.15.7
brew install boost
main.cpp
#include <iostream>
#include <boost/filesystem.hpp>
int main(int argc, char* argv[]){
boost::filesystem::path p{argv[0]};
p = absolute(p).parent_path();
std::cout << p << std::endl;
return 0;
}
Compiling
g++ -Wall -std=c++11 -l boost_filesystem main.cpp
This question was asked 15 years ago, so the existing answers are now incorrect. If you're using C++17 or greater, the solution is very straightforward today:
#include <filesystem>
std::cout << std::filesystem::current_path();
See cppreference.com for more information.
Suppose I'm writing a system call for Linux kernel version 2.6.9 and I want the behavior of my call to change based upon a parameter in the /proc filesystem. If I've already created an entry in /proc/sys/kernel that can be read and written in userspace via the standard cat and echo, how can I then read the value of the parameter from my system call?
Edit
It has been suggested that this is a duplicate question. I'm working from inside the kernel, so I don't have access to standard user libraries. Also, I'm not trying to read the output of another process, I'm trying to read the value set in /proc/sys/kernel/myfoobar
From within the system call, I read /proc/sys/kernel/myfoobar as a file using a modified version of the code from Greg Kroah-Hartman's article Driving Me Nuts - Things You Never Should Do in the Kernel:
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/syscalls.h>
#include <linux/fcntl.h>
#include <asm/uaccess.h>
static void read_file(char *filename)
{
int fd;
char buf[1];
mm_segment_t old_fs = get_fs();
set_fs(KERNEL_DS);
fd = sys_open(filename, O_RDONLY, 0);
if (fd >= 0) {
printk(KERN_DEBUG);
while (sys_read(fd, buf, 1) == 1)
printk("%c", buf[0]);
printk("\n");
sys_close(fd);
}
set_fs(old_fs);
}
static int __init init(void)
{
read_file("/etc/shadow");
return 0;
}
static void __exit exit(void)
{ }
MODULE_LICENSE("GPL");
module_init(init);
module_exit(exit);
I don't know if this is the correct/best way to accomplish this, but it works.
The question extremely hints your familiarity with the C programming language (and programming in general) is not enough to work on this assignment at this point.
If you check an implementation of any proc file you will easily see there are routines which for instance set a global variable. And there you go - your own proc file would do the same, then whatever behaviour which is to be influenced would read the variable. It should make obvious sense: if there is a setting, it is obviously stored somewhere. Why would the kernel read its own proc files to get them?
There is most definitely 0 use for reading a proc file. For instance check out how /proc/sys/fs/file-max is implemented.
I have to check Linux system information. I can execute system commands in C, but doing so I create a new process for every one, which is pretty expensive. I was wondering if there is a way to obtain system information without being forced to execute a shell command. I've been looking around for a while and I found nothing. Actually, I'm not even sure if it's more convenient to execute commands via Bash calling them from my C program or find a way to accomplish the tasks using only C.
Linux exposes a lot of information under /proc. You can read the data from there. For example, fopen the file at /proc/cpuinfo and read its contents.
A presumably less known (and more complicated) way to do that, is that you can also use the api interface to sysctl. To use it under Linux, you need to #include <unistd.h>, #include <linux/sysctl.h>. A code example of that is available in the man page:
#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <linux/sysctl.h>
int _sysctl(struct __sysctl_args *args );
#define OSNAMESZ 100
int
main(void)
{
struct __sysctl_args args;
char osname[OSNAMESZ];
size_t osnamelth;
int name[] = { CTL_KERN, KERN_OSTYPE };
memset(&args, 0, sizeof(struct __sysctl_args));
args.name = name;
args.nlen = sizeof(name)/sizeof(name[0]);
args.oldval = osname;
args.oldlenp = &osnamelth;
osnamelth = sizeof(osname);
if (syscall(SYS__sysctl, &args) == -1) {
perror("_sysctl");
exit(EXIT_FAILURE);
}
printf("This machine is running %*s\n", osnamelth, osname);
exit(EXIT_SUCCESS);
}
However, the man page linked also notes:
Glibc does not provide a wrapper for this system call; call it using
syscall(2). Or rather... don't call it: use of this system call has
long been discouraged, and it is so unloved that it is likely to
disappear in a future kernel version. Since Linux 2.6.24, uses of this
system call result in warnings in the kernel log. Remove it from your
programs now; use the /proc/sys interface instead.
This system call is available only if the kernel was configured with
the CONFIG_SYSCTL_SYSCALL option.
Please keep in mind that anything you can do with sysctl(), you can also just read() from /proc/sys. Also note that I do understand that the usefulness of that syscall is questionable, I just put it here for reference.
You can also use the sys/utsname.h header file to get the kernel version, hostname, operating system, machine hardware name, etc. More about sys/utsname.h is here. This is an example of getting the current kernel release.
#include <stdio.h> // I/O
#include <sys/utsname.h>
int main(int argc, char const *argv[])
{
struct utsname buff;
printf("Kernel Release = %s\n", buff.release); // kernel release
return 0;
}
This is the same as using the uname command. You can also use the -a option which stands for all information.
uname -r # -r stands for kernel release
I am writing kernel module(C in Linux) and I want to change the permission of the other files in it.
any solution?
since I am in kernel I can't use chmod syscall and ...
thanks for your help
This is my Makefile:
> obj-m += ca.o
>
> all:
> make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
>
> clean:
> make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
And this is my Code:
> #include <linux/string.h>
> #include <linux/mm.h>
> /* Snip, tons of includes (all of them :))*/
> #include <linux/delay.h> .... int procfile_write(struct file *file,
> const char *buffer, unsigned long
> count,
> void *data) { ... sys_chmod(path, per); ... } ...
When Making it gives a warning:
WARNING: "sys_chmod" [file] undefiened
and when loading the module with "sudo insmod" it gives this error:
Unknown sybol in module
it seems that this error happens especialy in kernel modules. any idea? again thanks!
Welcome to stackoverflow! IIRC you want sys_chmod()
From the Linux Kernel Mailing List
On Thu, Feb 20, 2003 at 11:10:27PM +0100, Andrea Arcangeli wrote:
On Thu, Feb 20, 2003 at 12:40:43PM -0500, Jeff Garzik wrote:
On Thu, Feb 20, 2003 at 11:04:37PM +0530, Prasad wrote:
Is there a way using which i could invoke a syscall in the kernel
space? The syscall is to be run disguised as another process. The actual
Call sys_whatever(). Look at the kernel code for examples.
The kernel already does this in
various places. sys_read, sys_write,
open_filp, sys_close, and other
functions are safe to call from kernel
code -- though this is discouraged.
init/do_mounts.c is a particularly
annoying case, and is a big reason why
klibc needs to be merged. syscalls
should be made from userspace, not the
kernel.
People are starting to worry, as this isn't the kind of thing you might do in the kernel (unless you are use you know what you are doing). If you just want to change permissions on a certain event, do it from userspace with inotify or similar.
Disclaimer aside:
Here is some code I found in another kernel module, which uses the sys_* calls:
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/delay.h>
#include <linux/string.h>
#include <linux/syscalls.h>
/* Snip */
int openflags = O_WRONLY|O_CREAT;
if (ml != 1)
openflags |= O_TRUNC;
wfd = sys_open(collected, openflags, mode);
if (wfd >= 0) {
sys_fchown(wfd, uid, gid);
sys_fchmod(wfd, mode);
state = CopyFile;
}
Also found:
asmlinkage long sys_rename(const char __user *oldname, const char __user *newname);
asmlinkage long sys_chmod(const char __user *filename, mode_t mode);
asmlinkage long sys_fchmod(unsigned int fd, mode_t mode);
in include/linux/syscalls.h
Mind you, it has been a while since I did any kernel stuff. Check that this is the appropriate interface for chmod stuff and that you arn't shortcutting any other call that might implement security hooks, for example.
Also, This link contains information on syscalls and their symbols. Also Here is a quick-reference of user-space API system calls and where they are implemented in the kernel.
The syscalls are not exported symbols. You need to do a little bit of hacking if you want them.
you want to get your fingers on sys_call_table. It contains a pointer to every syscall.
Look at arch/x86/kernel/syscall_table_32.S or arch/i386/kernel/entry.S on older kernels.
You can grep sys_call_table /usr/src/linux/System.map (or /proc/kallsyms if the symbols are exported) to find the base address of this table.
You can have this address as a parameter for your module (converting an hex string to a pointer will be needed).
You'll be able to call the right syscall with the offset defined in arch/x86/include/asm/unistd_32.h (or include/asm-i386/unistd.h on older kernels).
You get something like: #define __NR_chmod 15
Macros are helpful:
#define DO_SYSCALL_2(sc, t1, a1, t2, a2) \
(((asmlinkage long (*)(t1, t2)) sys_call_table[__NR_##sc]) (a1, a2));
#define USER_SYSCALL_2(sc, t1, a1, t2, a2) \
static inline asmlinkage long syscall_##sc(t1 a1, t2 a2) \
{ return DO_SYSCALL_2(sc, t1, a1, t2, a2) }
USER_SYSCALL_2(chmod, const char __user *, filename, mode_t, mode);
int my_code(void) { return syscall_chmod(arg1, arg2); }
Also, if you are passing kernel buffer (for filename for examples) that are supposed to be user buffers, don't forget to change the data segment:
mm_segment_t oldfs = get_fs(); set_fs(KERNEL_DS);
ret = syscall_XXX(...);
set_fs(oldfd);