How to move a particular file from one folder to another folder?
What I have tried,
#include <stdio.h>
int main() {
FILE *tFile;
if (tFile != NULL)
tFile = NULL;
if ((tFile = fopen("TempFile.txt", "rw")) == NULL) {
return -1;
}
mv("TempFile.txt", "../MST");
printf("Done Succesfully\n");
return 0;
}
Error :
test.c:17:2: warning: no newline at end of file
/tmp/ccKLWYNa.o(.text+0x5e): In function `main':
: undefined reference to `mv'
collect2: ld returned 1 exit status
Please guide me how can I do this.
You really should read Advanced Linux Programming and syscalls(2)
To move (from C) a file from one place to another in the same file system just use the rename(2) syscall.
At the very least, for your particular example, you'll need to code:
char* srcpath = "TempFile.txt"; // assume it is a variable path
char destpath[1024];
snprintf (destpath, sizeof(destpath), "../MST/%s", srcpath);
if (rename (srcpath, destpath)) {
// something went wrong
if (errno == EXDEV) {
// copy data and meta data
} else { perror("rename"); exit(EXIT_FAILURE); };
}
else { // the rename succeeded
}
If you really want to mv TempFile.txt ../MST/TempFile.txt specifically for TempFile.txt only you could just call rename("TempFile.txt", "../MST/TempFile.txt") and handle the error cases like I suggest. If you are sure that ../MST/lie in the same file system than . then EXDEV should not happen and you don't need to handle it particularly (but you do need to handle errors).
If you want to move a file between two different file systems, you have to copy the data (and perhaps some of the meta-data) yourself (and then remove e.g. with unlink(2)) the original source file). You could detect that situation by various means: you could just try the rename and if errno (see errno(3)) is EXDEV you need to copy the file. Or you could use stat(2) to query the source file(and the destination directory) meta-data -e.g. its size and its file system.
Of course, you need to understand what are files on Linux (or Posix), in particular what is an inode.... See inode(7) and credentials(7)
You could have used system with /bin/mv (but be careful about strange characters -like spaces or semicolons- in the file paths, you need to escape them to avoid code injection), apparently you don't want to.
You should play with strace(1) (or perhaps also ltrace) on mv in various situations to understand what it is doing. Also, study the source code of GNU coreutils which provides /bin/mv notably in mv.c ...
Some extra C or C++ libraries may provide you with functions to move files (in the same filesystem they should do a rename, in different file systems they copy the source file data and perhaps some meta-data and unlink the source, so cannot be atomic), e.g. in C g_file_move (from Gio with Glib from Gnome), or in C++ copy_file -followed by remove in Boost, etc etc....
PS. For temporary files see tmpfile(3), mkstemp(3), etc...
Related
These terms may not be 100% accurate, but I'm using the GCC compiler and POSIX library. I have C code compiled with the SQLite amalgamation file to a single executable.
In the user interface that exchanges JSON messages with the C program, I'd like to make it possible for users to copy the SQLite database files they create through the C program, and copy a full directory/folder.
Thus far, I've been able to rename and move files and folders programmatically.
I've read many questions and answers here, at Microsoft's C runtime library, and other places but I must be missing the fundamental points. I'm using regular old C, not C++ or C#.
My question is are there POSIX functions similar to rename(), _mkdir(), rmdir(), remove(), _stat(), that allow for programmatic copying of files and folders in Windows and Linux?
If not, can one just make a new folder and/or file and fread/fwrite the bytes from the original file to the new file?
I am primarily concerned with copying SQLite database files, although I wouldn't mind knowing the answer in general also.
Is this answer an adequate method?
Is the system() function a poor method? It seems to work quite well. However, it took awhile to figure out how to stop the messages, such as "copied 2 files" from being sent to stdout and shutting down the requesting application since it's not well-formed JSON. This answer explains how and has a link to Microsoft "Using command redirection operators". A /q in xcopy may or may not be necessary also, but certainly didn't do the job alone.
Thank you very much for any direction you may be able to provide.
The question that someone suggested as an answer and placed the little submission box on this question is one that I had already linked to in my question. I don't mean to be rude but, if it had answered my question, I would not have written this one. Thank you whoever you are for taking the time to respond, I appreciate it.
I don't see how that would be a better option than using system() because with the right parameters all the sub-directories and files of a single parent folder can be copied in one statement without having to iterate through all of them manually. Is there any reason why it would not be better to use system() apart from the fact that code will need to be different for each OS?
Handling errors are a bit different because system() doesn't return an errno but an exit code; however, the errors can be redirected from stderr to a file and pulled from there, when necessary
rename(): posix
_mkdir(): not posix. You want mkdir which is. mkdir takes two arguments, the second of which should usually be 077.
rmdir(): posix
remove(): posix
_stat(): not posix, you want stat() which is.
_stat and _mkdir are called as such on the Windows C library because they're not quite compatible with the modern Unix calls. _mkdir is missing an argument, and _stat looks like a very old version of the Unix call. You'll have trouble on Windows with files larger than 2GB.
You could do:
#ifdef _WIN32
int mkdir(const char *path, int mode) { return _mkdir(path); } /* In the original C we could have #defined this but that doesn't work anymore */
#define stat _stat64
#endif
but if you do so, test it like crazy.
In the end, you're going to be copying stuff with stdio; this loop works. (beware the linked answer; it has bugs that'll bite ya.)
int copyfile(const char *src, const char *dst)
{
const int bufsz = 65536;
char *buf = malloc(bufsz);
if (!buf) return -1; /* like mkdir, rmdir, return 0 for success, -1 for failure */
FILE *hin = fopen(src, "rb");
if (!hin) { free(buf); return -1; }
FILE *hout = fopen(dst, "wb");
if (!hout) { free(buf); fclose(hin); return -1; }
size_t buflen;
while ((buflen = fread(buf, 1, bufsz)) > 0) {
if (buflen != fwrite(buf, 1, buflen)) {
fclose(hout);
fclose(hin);
free(buf);
return -1; /* IO error writing data */
}
}
free(buf);
int r = ferror(hin) ? -1 : 0; /* check if fread had indicated IO error on input */
fclose(hin);
return r | (fclose(hout) ? -1 : 0); /* final case: check if IO error flushing buffer -- don't omit this it really can happen; calling `fflush()` won't help. */
}
I fully understand that tmpnam has been deprecated and would like to remove it from a function in an existing file that prevents me from building the project. However, since I am not familiar with it and am unable to experiment with it, I am not sure how best to replicate this functionality.
if ((myfileName = tmpnam(NULL)) == NULL) { return APP_ERROR }
I read the information on tmpnam here but the best I can come up with is to use something like:
if (tmpnam_r == NULL) { return APP_ERROR }
However, since I cannot compile with tmpnam and am unfamiliar with the code in question, I am not confident in properly capturing the original intent.
As best as I can tell, this appears to be testing if the file exists, and if not, simply returns an error, as the next step consists of copying content into myfileName, which should presumably exist following the above check.
The problem with tmpnam() is that it generates a name that is unique and does not exist when it returns, but that name is not guaranteed to be unique by the time you use it in a call to fopen() (or open()).
The key feature of the mkstemp() function is that it creates and opens a file with the new name, so that there isn't a TOCTOU (time of check, time of use) vulnerability. This cuts down the avenues for security risks.
Code designed to use tmpnam() usually needs a file name, so using tmpfile() is usually not an option; it doesn't provide a way to find the file name. If you don't need the file name then using tmpfile() works well and is Standard C, so it is widely available.
The specific case of tmpnam() and tmpnam_s() is interesting. Although tmpnam_s() avoids some string-related problems, it does not change the behaviour of tmpnam() in the way that causes the security problems addressed by mkstemp(). So, independent of the portability issues that arise from attempting to use tmpnam_s() (or any of the other *_s() functions from Annex K of the C11 or C18 standards), it doesn't fix the problem that causes tmpnam() to be deprecated.
You can arrange to use mkstemp() instead of tmpnam() and close the file descriptor before continuing with the other code:
tmpnam(name); // Replace this
int fd = mkstemp(name); // With this…
if (fd >= 0)
close(fd);
It's not great, but it does ensure the file is created, which reduces the security vulnerabilities a bit, but not as much as using the file descriptor directly. You could (should) wrap that into a function.
Note that the mkstemp() returns a file descriptor; if you want a file stream, you can use fdopen() to create a file stream from the file descriptor. And if that fails, you probably want to remove the file (with remove() or unlink()).
So, that gives you a need for fmkstemp():
#include <stdio.h>
#include <stdlib.h> /* mkstemp() */
#include <unistd.h> /* close() */
extern FILE *fmkstemp(char *name); /* Add to a convenient header file */
FILE *fmkstemp(char *name)
{
int fd = mkstemp(name);
FILE *fp = 0;
if (fd >= 0)
{
fp = fdopen(fd, "w+");
if (fp == 0)
{
close(fd);
unlink(name);
}
}
return(fp);
}
Note that after you've used fmkstemp(), you use fclose() to close the file stream (and, behind the scenes, that closes the file descriptor).
Don't forget to remove the temporary file before exit. That's where a function registered with atexit() or one of its variants can be useful.
I'm trying to learn File I/O concepts in C programming language. I'm using GNU / Linux ( Ubuntu 16.04 LTS ) and my IDE is eclipse 3.8. when I try to write in a file through fprintf() method, it doesn't create any files or if the file is even created, it doesn't write in it. I tried to fix the problem by using fflush() or setbuf(file_pointer, NULL) methods as is suggested here but still no change. I guess I'm writing the address of the file in a wrong way.
Here is the code:
#include <stdio.h>
int main(void){
FILE *file_pointer;
file_pointer=fopen("~/.textsfiless/test.txt","w+");
setbuf(file_pointer,NULL);
fprintf(file_pointer,"Testing...\n");
fclose(file_pointer);
return EXIT_SUCCESS;
}
Can someone explain what's wrong here?
On Linux, the ~ in ~/.textsfiless/test.txt is not expanded by the C library fopen... When you use ~ on the command line, it is expanded by your shell (but not by the program using it, started by the shell doing some execve(2)...) into your home directory; the expansion is called globbing. Read glob(7). You are very unlikely to have a directory named ~.
You should read Advanced Linux Programming
So you should check if fopen failed (it is very likely that it did fail). If you want to get a file in the home directory, you'll better use getenv(3) with "HOME" (or perhaps getpwuid(3) & getuid(2)...). See environ(7)
Perhaps a better code might be:
char*homedir = getenv("HOME");
if (!homedir) { perror("getenv HOME"); exit(EXIT_FAILURE); };
char pathbuf[512]; /// or perhaps PATH_MAX instead of 512
snprintf(pathbuf, sizeof(pathbuf),
"%s/.textsfiless/test.txt", homedir);
FILE *file_pointer = fopen(pathbuf, "r");
if (!file_pointer) { perror(pathbuf); exit(EXIT_FAILURE); };
and so on.
Notice that you should check against failures most C standard library (& POSIX) functions. The perror(3) function is useful to report errors to the user on stderr.
(pedantically, we should even test that snprintf(3) returns a length below sizeof(pathbuf) or use and test against failure asprintf(3) instead; I leave that test as an exercise to the reader)
More generally, read the documentation of every external function that you are using.
Beware of undefined behavior (your code is probably having some, e.g. fprintf to a NULL stream). Compile your code with all warnings & debug info (so gcc -Wall -g) and use the gdb debugger. Read What every C programmer should know about undefined behavior.
BTW, look into strace(1) and try it on your original (faulty) program. You'll learn a lot about the system calls used in it.
Most likely your call to fopen() fails. You don't have any checking in your program to ensure fopen even worked. It may not have, and this could be due to a variety of things, like you spelling the path wrong, wrong file or process permissions, etc.
To see what really happened, you should check fopen's return value:
#include <stdio.h>
int main(void){
FILE *file_pointer;
file_pointer=fopen("~/.textsfiless/test.txt","w+");
if (file_pointer == NULL) {
printf("Opening the file failed.");
return EXIT_FAILURE;
}
setbuf(file_pointer,NULL);
fprintf(file_pointer,"Testing...\n");
fclose(file_pointer);
return EXIT_SUCCESS;
}
Edit: Since your comment, you getting the path wrong is most certainly what happened. If you're executing your program from the current directory, and your file is in a folder called "textfiless" in your current directory and your file is called "test.txt", then you'd call fopen like this:
file_pointer=fopen("/textsfiless/test.txt","w+");
I am trying to open a text file with C++ in Mac OS X but I always get a Bus error.
I do not care where to put the file. I just need to read it. Am I writing its address wrong? or that Bus Error has another reason?
FILE *dic;
dic = fopen("DICT","rb");
dic = fopen("./DICT","rb");
dic = fopen("~/DICT","rb");
dic = fopen("~//DICT","rb");
With a little bit of clarification I see the problem in your C code (not C++!) is that fopen() returns NULL. You can check what the problem really is by reporting the detailed error:
if( (dic = fopen("DICT", "rb") == NULL ) {
fprintf(stderr, "%s\n", perror("ERROR:"));
exit(1);
}
If fopen() fails to find the file on the user's desktop and you wish your code to work on multiple platforms then you might define a function to get the user's desktop directory for using with fopen(). Something like
char* user_desktop(char* buf, size_t len)
{
const char* const DESKTOP_DIR =
#ifdef PC
"C:\\Documents and Settings\\Pooya\\Desktop\\"
#elif defined(OSX)
"/Users/Pooya/Desktop/"
#elif defined(LINUX)
"/home/users/pooya/Desktop/"
// fail to compile if no OS specified ...
#endif
return strncpy(buf, DESKTOP_DIR, len);
}
You probably want to look into a more robust way of getting the path of the desktop for each operating system. Most operating systems have an API for this, so do your research. There are also more robust ways of splitting behaviour for various platforms, you can look into that or open a different question about that. I just wanted to express my idea, of having a function which will return you the appropriate desktop path no matter on which platform you compile your code.
This code is correct! Pay attention to the directory where the executable is located. For sure the directory of the execution is not the same as you are expecting (I suppose, the directory of the .c files, right?).
I believe you are executing the app from the IDE. This is commom in Xcode, it mounts the exec`s in another location than that where the project files are located, and this such location that is considered when you execute the program, whether you execute it from the IDE or not!
Simply move the file you want to read to the location of the application and it will work properly.
Is there a way to retrieve path information from a file descriptor or FILE pointer?
I'm aware that this data may not always be relevant/useful for case where the file descriptor is a socket, pipe, etc.
I don't believe there's any portable way, but e.g. on Linux you can call readlink on "/proc/self/fd/fileno" and the kernel will give you a path if it can, or one of various kinds of funny-looking strings if not.
If you're lucky enough to be using Mac OS X you can use the following code:
#define _DARWIN_C_SOURCE
#include <sys/fcntl.h>
.
.
.
char pathbuf[PATH_MAX];
if (fcntl(fd, F_GETPATH, pathbuf) >= 0) {
// pathbuf now contains *a* path to the open file descriptor
}
Note that the path you get back is not necessarily the one used to open the file... If there are hard links, especially, the path you get back will be a valid path to the file.
There can be one or many names for a file, so no std way.
I am not sure if there can be something OS specific.