This is the first time I'm coding C in Windows and a weird bug is driving me crazy.
I'm trying to open a .txt file using fopen, and it keeps giving me the "file doesn't exist" error (it also gave me the "no permission" error, once).
My code is as follows (doesn't get any simpler than that):
FILE *file;
if((file=fopen("C:\\Users\\ste\\Desktop\\file.txt", "r"))==NULL)
{
printf("Cannot open file.\n");
puts(strerror(errno));
getchar();
exit(1);
}
Am I missing something here? Thanks in advance!
I bet you have the Windows "hide extensions" bugfeature turned on. So the file which is really called "file.txt" appears in your Explorer as "file". And if it appeared to be "file.txt" in the Explorer, it would have to be named "file.txt.txt" on the hard drive.
The code itself is fine assuming what it does is what you are wanting.
"r" requires that the file already exists (it wont create one for you) so you need to make sure that the path is correct. Is the desktop path right, not on another drive etc?
The permission error would occur if it was executed by a user other than "ste", or of course if somthing had changed the permissions on that file path some how to prevent access.
Related
This code does not open file properly, it returns no such file or directory, although the path and privilege are there and no other program is using the file. How can I fix the error? I tried swapping the path and moving the file, the error is there still.
char string[105];
FILE* file = fopen("C:\\Users\\Public\\Documents\\a.txt", "r");
while (fgets(string, 100, file)) {
printf("%s", string);
}
It can be surprisingly tricky to open a simple file! Lots of things can go wrong. I recommend writing slightly more verbose code, like this:
#include <string.h>
#include <errno.h>
char* filename = "C:\\Users\\Public\\Documents\\a.txt";
char string[105];
FILE* file = fopen(filename, "r");
if (file == NULL) {
fprintf(stderr, "can't open %s: %s\n", filename, strerror(errno));
exit(1);
}
while (fgets(string, 100, file)) {
printf("%s", string);
}
The point is that the error message prints out both the name of the file it tried but failed to open, and the actual reason it couldn't open it. (Also, by storing the filename in a variable, you make it absolutely certain that the filename it prints in the error message is the filename it tried but failed to open.) It sounds like you already know that the error was "no such file or directory", but I'm not sure how you know this.
Even though I've been programming in C for a long time, sometimes I still have this problem. One thing I'll sometimes do is use my mouse to copy the exact filename string printed in the error message, the file the program said it couldn't open, the file I'm sure is really there, and paste it into a terminal window (or CMD or Powershell if you're on Windows), along with a directory-listing command, to see if the operating system can actually see the file. That is, for your example, the command I'd run is
dir C:\Users\Public\Documents\a.txt
but the point is that I would not actually type the pathname "C:\Users\Public\Documents\a.txt", instead I would copy and paste it out of the error message that the program printed. Sometimes there are surprising little impossible-to-spot differences between the filename you thought it was trying to open, versus the filename it was actually trying to open, and this exercise is a good way to let the computer help you find those differences.
Remember, too, that you'll get the error "No such file or directory" if there's no file by that name in the directory, or if the directory isn't there at all. For example, if you're trying to open the path
C:\Users\Public\Documents\a.txt
and the file a.txt keeps not being there, and you keep checking your home directory
C:\Users\Donkey\Documents
and you keep seeing that the file is there, it can be surprisingly easy to overlook what the real problem is. :-)
Addendum: You might be having an issue with the different Unix/Linux versus Windows file path separators, that is, / versus \. Usually, on a Windows machine, it's safest to use \, as you've done. (One very frequent mistake is to forget to double the backslashes, but it looks like you got that right.) Depending on your programming environment, if there's some level of Unix emulation going on, you can sometimes use Unix-style /, and it will automatically translate to \ for you. I've never heard of a situation where using \ made it not work (which is a possibility being explored in the comments), but you might experiment with that, perhaps trying
char* filename = "/c/Users/Public/Documents/a.txt";
or (less likely)
char* filename = "C:/Users/Public/Documents/a.txt";
I have an application developed in C. This application is supported across multiple platforms. There is one functionality where we are transferring files via file transfer protocol to different machine or to any other directory on local machine. I want to include a functionality where I can transfer the file with some temporary name and once the transfer is complete, I want to rename the file with the correct name (the actual file name).
I tried using simple rename() function. It works fine in Unix and Linux machines. But it does not work on Windows. It is giving me an error code of 13(Permission denied error).
First thing, I checked in msdn to know the functionality of rename if I have to grant some permissions to the file etc.
I granted full permissions to the file (lets say it is 777).
I read in few other posts that I should close the file descriptor before renaming the file. I did that too. It still gives the same error.
Few other posts mentioned about the owner of the file and that of the application. The application will run as a SYSTEM user. (But this should not affect the behavior, because I tried the same rename function in my application as follows:
This works fine from my application:
rename("C:/abc/aaa.txt","C:/abc/zzz.txt");
but
rename(My_path,"C:/abc/zzz.txt");
doesn't work, where My_path when printed displays C:/abc/test.txt.
How can I rename a file? I need it to work on multiple platforms.
Are there any other things I should be trying to make it work.?
I had this same problem, but the issue was slightly different. If I did the following sequence of function calls, I got "Permission Denied" when calling the rename function.
fopen
fwrite
rename
fclose
The solution was to close the file first, before doing the rename.
fopen
fwrite
fclose
rename
If
rename("C:/abc/aaa.txt","C:/abc/zzz.txt");
works but
rename(My_path,"C:/abc/zzz.txt");
does not, in the exact same spot in the program (i.e. replacing one line with another and making no changes), then there might be something wrong with the variable My_path. What is the type of this variable? If it is a char array (since this is C), is it terminated appropriately? And is it exactly equal to "C:/abc/aaa.txt"?
(I wish I could post this as a comment/clarification rather than as an answer but my rep isn't good enough :( )
I'm programming in C, and
I have the following problem:
I use fopen and try to read from a csv file, that is currently storred in the folder of the exe file of the program.
the program works fine in debug mode and release mode, but when I try to run the program in "start without debugging" on visual studio 2008 express edition, the program stops working and windows is showing a message: "*.exe has stopped working. a program caused the program to stop working correctly. windows will close the program and notify you if a solution is available".
I've tried running the program on several computers, and it's the same.
another information I can give you is that if I enter the full path of the file (C:....file.csv) - then is works just fine, without any problem.
I know I didn't write any code, but I hope someone will have an idea why this can happend.
thanks is advance.
Your program is not finding the csv file, fopen() fails and return a null pointer, you try to use it without checking and your program crashes (just my guess).
Firstly, you must make a check to see if fopen() could indeed open your file:
FILE* f = fopen("file.csv", "r");
if(f == NULL) {
/* print some meaningful error */
} else {
/* use the file */
}
Secondly, you may solve the problem by executing your program from the same folder the file is present. I am not a Windows guy, but if you create a link to the ".exe", in its properties may have some configuration called "Working Directory" or something like that, that you may set to the path on where the file can be found.
Every process has a working directory, that is usually the directory from where it was started, though it may be inherited from the parent process and it may be changed programmatically. If you do not specify the full path when loading a file, the process will search for the file in its current working directory.
I have some code which iteratively appends data to a file and looks similar to:
for(int i=0; i<number; i++){
FILE *log_file;
char name[50];
sprintf(name,"something_%d.log",i);
log_file=fopen(name,"a");
if(log_file == NULL){
printf("ERROR cannot open file %s",name);
abort();
}
/* Write stuff to file */
fclose(log_file);
}
Seems simple enough right? If the file exists and I have permission to write to it, it proceeds as normal; if the file does not exist and I have permission to write files in the directory, it creates the file as normal. WRONG! Somehow, when I come across a particular file name (MINI_3f_1_0.log) the program cannot create/open the file and yields log_file = NULL. Obviously this is not my entire code, and the worst thing is that I cannot reproduce this problem with a simple program as shown.
I have already spent a few hours trying to track down what is going on, and so far I am 100% sure of the following:
The file is declared, opened, and closed within the same scope
A file of the same name is not open in any other function/the entire program
I have permission to read/write in the directory
Trying to open the file out of the iterative order produces the same error when it is done in the same routine
Any guidance you guys/gals can give me would be greatly appreciated. If you have come across anything like this in your experience, how did you fix it?
As suggested by Mat in the comments,running the code in a different directory did not produce the error. There is something likely wrong with the file system and needs to be looked into by the sys-admin.
I've been wondering about this one. Most books I've read shows that when you open a file and you found that the file is not existing, you should put an error that there's no such file then exit the system...
FILE *stream = NULL;
stream = fopen("student.txt", "rt");
if (stream==NULL) {
printf(“Cannot open input file\n”);
exit(1);
else {printf("\nReading the student list directory. Wait a moment please...");
But I thought that instead of doing that.. why not automatically create a new one when you found that the file you are opening is not existing. Even if you will not be writing on the file upon using the program (but will use it next time). I'm not sure if this is efficient or not. I'm just new here and have no programming experience whatsoever so I'm asking your opinion what are the advantages and disadvantages of creating a file upon trying to open it instead of exiting the system as usually being exampled on the books.
FILE *stream = NULL;
stream = fopen("student.txt", "rt");
if (stream == NULL) stream = fopen("student.txt", "wt");
else {
printf("\nReading the student list directory. Wait a moment please...");
Your opinion will be highly appreciated. Thank you.
Because from your example, it seems like it's an input file, if it doesn't exist, no point creating it.
For example if the program is supposed to open a file, then count how many vowels in it, then I don't see much sense of creating the file if it doesn't exist.
my $0.02 worth.
Argument mode:
``r'' Open text file for reading.
``r+'' Open for reading and writing.
``w'' Truncate file to zero length or create text file for writing.
``w+'' Open for reading and writing. The file is created if it does not
exist, otherwise it is truncated.
``a'' Open for writing. The file is created if it does not exist.
``a+'' Open for reading and writing. The file is created if it does not
exist.
Your question is a simple case. Read above description, when you call fopen(), you should decide which mode shall be used. Please consider why a file is not created for "r" and "r+", and why a file is truncated for "w" and "w+", etc. All of these are reasonable designs.
If your program expects a file to exist and it doesn't, then creating one yourself doesn't make much sense, since it's going to be empty.
If OTOH, your program is OK with a file not existing and knows how to populate one from scratch, then it's perfectly fine to do so.
Either is fine as long as it makes sense for your program. Don't worry about efficiency here -- it's negligible. Worry about correctness first.
You may not have permission to create/write to a file in the directory that the user chooses. You will have to handle that error condition.