#include <stdio.h>
#include <stdlib.h>
int main()
{
char c[1000];
FILE *fptr;
if ((fptr = fopen("program.txt", "r")) == NULL)
{
printf("Error! opening file");
// Program exits if file pointer returns NULL.
exit(1);
}
// reads text until newline
fscanf(fptr,"%[^\n]", c);
printf("Data from the file:\n%s", c);
fclose(fptr);
return 0;
}
Output is Error! opening file
I have program and txt file in same dir.
How can I direct access to that file?
To diagnose, use the system command to issue a ls or dir depending on your platform. That will tell you where you are running from. Odds are it is a different location than the files you are trying to open.
As suggested in the comment, try replacing printf with perror
if ((fptr = fopen("program.txt", "r")) == NULL)
{
perror("Error");
// Program exits if file pointer returns NULL.
exit(1); // Exiting with a non-zero status.
}
perror prototype is
void perror(const char *str)
where str is the C string containing a custom message to be printed before the error message itself.
However some causes of the of the file not being read are
File is not present in the current working directory. If this is the case, rectifying the path should fix the issue.
The program might not have the permissions to read from the file usually because of a setting related to discretionary access control. Perhaps do a chmod with file?
I made a quick run of your program on TURBOC++ by Borland and it executed without complaining any sort of Warning or Error
As mentioned in the earlier posted answers, you should replace printf by perror
CURRENT REPLACE BY
printf("Error! opening file"); perror("Error! Opening File.");
As in your case of file not found printf("Error! opening file"); will result in :
Error! Opening file.
However in case of perror("Error! Opening File."); if the file program.txt does not exist, something similar to this may be expected as program output
The following error occurred: No such file or directory
The difference is obvious from above explanations.
Regarding your program, I am making an assumption that either your path to the file is wrong or there is some problem with your compiler.
Try to open your file in w+ mode also to ensure that the file exist.
Related
I have this code work :
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main()
{
FILE *File_fp = fopen("Example.dat", "w");
char Temporary[50];
if(!File_fp)
{
printf("An error occurred while creating the file.\n");
exit(1);
}
fprintf(File_fp, "This is an example.\n");
fgets(Temporary, 49, File_fp);
printf("It was \"%s\"\n", Temporary);
return EXIT_SUCCESS;
}
I printed "This is an example." in the file, "Example.dat" and I want to read it again from the file by code above but there's no string in the output. Why? Please help me.
You are opening the file in write-only mode ("w"). Use "w+" for reading and writing.
FILE *File_fp = fopen("Example.dat", "w+");
To read a file, you have to use the mode "r". Example:
FILE *File_fp = fopen("Example.dat", "r");
And you made a mistake in this code. If it fails to create a file, fopen() function will return NULL. Then the value of the file pointer would be NULL.
So, in your code if section will execute when the file is successfully created. So, change your code like this:
if(File_fp)
{
printf("An error occurred while creating the file.\n");
exit(1);
}
Just remove the (!) logical not sign.
Trying to open and write to the following file path, for some reason it is not opening, I've tried several different paths and nothing has worked. I am running this from C:\
FILE* fptwo = fopen("\\C:\\Program Files\\NotMal.txt", "w");
if (fptwo != NULL)
{
printf("open progfiles successful \n");
//add this text to the file
fprintf(fptwo, "This is text");
printf("add text succuessful \n");
//close file pointer when finished
fclose(fptwo);
}
*please feel free to delete or close this question if it is answered somewhere else, I apologize for the mistakes made within this, and if it is a stupid error.
You test if you have correctly opened the file, it's good !
But it's better to know why your function call have failed.
For "fopen", you can know by looking the value of errno. (read the man about fopen).
And a "cool thing" is that you can obtain an english description by using "strerror".
So, just do :
#include <string.h> // For strerror
#include <errno.h> // For .... errno
FILE* fptwo = fopen("\\C:\\Program Files\\NotMal.txt", "w");
if (fptwo == NULL)
{
printf("Error : errno='%s'.\n", strerror(errno));
}
else
{
printf("open progfiles successful \n");
//add this text to the file
fprintf(fptwo, "This is text");
printf("add text succuessful \n");
//close file pointer when finished
fclose(fptwo);
}
Program Files is windows default software deployment folder. Better not to use that path. Better create your own test folder and test. If possible not to name folder with space.
FILE* fptwo = fopen("C:\\MyProject\\test\\NotMal.txt", "w");
Im supposed to write a program that opens an excel file, reads the numbers on the file, multiplies them by 9.8 and the shows the answer in another excel gile.
I wrote this, and I did not get any errors in the compiler, but when I run it, it does not open any files. How do I make it open the files?
#include <stdio.h>
int main() {
FILE *archivo;
FILE *archivoSalida;
int masa;
float peso;
archivo = fopen("C:/Users/nacho/Documents/UNAM/Informatica/proyecto/archivoEntrada.txt", "r");
archivoSalida = fopen("C:/Users/nacho/Documents/UNAM/Informatica/proyecto/archivoSalida.txt", "r");
if (archivo != NULL)
{
printf("The file was opened succesully");
while (fscanf(archivo,"%d", &masa)!= EOF)
{
peso=masa*9.81;
fprintf(archivoSalida, "%f\n", peso);
}
}
else
{
printf ("Error");
}
fclose(archivo);
fclose(archivoSalida);
return 0;
}
You'll want to fopen the output file ("archivoSalida") with mode "w" (for write) instead of "r" (for read). See e.g. http://pubs.opengroup.org/onlinepubs/009695399/functions/fopen.html.
You do check if the input file could be opened (if (archivo != NULL)). Why don't you do the same for the output file?
Upon an error, you should output which error occured from errno, e.g. via perror(...). That should help in finding the actual problem.
Your file denominated by archivoSalida is opened in read mode ('r').
You should also check the return codes of read/writes functions to be sure everything happen as wanted.
The file names look Windows-ish. Is it possible that all of the forward slashes (/) that you have in both file names should really be back slashes (\)?
Apparently, there's no data regarding my question (I tried searching it out here but none of the threads I've read answered my doubt). Here it is: I'm trying desperately to figure out how can I put a correct path into the fprintf function and none of my tries have been successful. Here's the program:
#include <stdio.h>
#include <stdlib.h>
int main(){
FILE *fp = NULL;
//opening the file
fp = fopen("C:/Users/User1/Desktop/myfile.txt", "w+");
//if there's an error when opening the file, the program shuts down
if(fp == NULL){
printf("error");
exit(EXIT_FAILURE);
}
//print something on the file the program just opened (or created if not already existent)
fprintf(fp, "to C or not to C, that is the question");
//closing the file
fclose(fp);
//end of main function
return 0;
}
My question is: why my program always shuts down? What am I doing wrong? It's just a Windows problem (I saw that, on the User1 folder icon, there's a lock, could be a permission denied thing?) or I'm just putting the path in an incorrect way? I tried to use a string to save the path, I tried to change the opening mode, I even tried to disable all the antiviruses, antimalwares and firewalls I have installed on my computer but nothing, the program still doesn't create the file where I want it.
P.S. Sorry for bad English.
P.P.S. Sorry if a similar question has been already posted, I didn't manage to find it.
fp = fopen("C:\Users\User1\Desktop\myfile.txt", "w+");
The character \ is the escape character in C. You must escape it:
fp = fopen("C:\\Users\\User1\\Desktop\\myfile.txt", "w+");
Even better, windows now supports the / directory separator. So you can write:
fp = fopen("C:/Users/User1/Desktop/myfile.txt", "w+");
With no need to escape the path.
Reference:
MSDN fopen, specifically the Remaks section
Use perror() to have the Operating System help you determine the cause of failure.
#define FILENAME "C:/Users/User1/Desktop/myfile.txt"
fp = fopen(FILENAME, "w+");
// report and shut down on error
if (fp == NULL) {
perror(FILENAME);
exit(EXIT_FAILURE);
}
I am working through the excellent The C Programming Language at the moment, and have got stuck while trying to open and read a file. The program compiles, but seg faults on execution:
$ ./a.out
Segmentation fault
Here is the code:
#include <stdio.h>
main()
{
FILE *fp;
fp=fopen("/home/c-sandbox/index.html", "r");
fprintf(fp, "Testing...\n");
fclose(fp);
}
Note that the path points to a real file containing the string "hello, world".
Any ideas on where I am going wrong?
Make sure fp is not NULL before trying to write to it. For example:
if(fp == NULL)
{
fprintf(stderr, "Cannot open file\n");
return EXIT_FAILURE; // defined in stdlib.h
}
You need to open the file with something other than "r", which only allows file reading. Read the man page for fopen to find out which mode would work the best for you. Example:
"w" - Truncate to zero length or create file for writing.
"a" - Append; open or create file for writing at end-of-file.
You opened the file for reading only, and are attempting to write to it.
Use "a" if you want to append to the end of the existing file.
Edit: As others have noted, you're also not checking to see if the file was opened. fopen will return NULL if it fails and set the global variable errno to a value that indicates why it failed. You can get a human-readable explanation using strerror(errno)
if( fp == NULL ) {
printf( "Error opening file: %s\n", strerror( errno ) );
}
You are opening it in readonly mode! Need to use w or a for writing/appending to the file :)
fopen("/home/c-sandbox/index.html", "w");
You should check that fopen does not return NULL. I suspect it is returning NULL and either the fprintf and/or fclose calls are getting messed up.
#include <stdio.h>
main()
{
FILE *fp;
fp=fopen("/home/c-sandbox/index.html", "r");
if(!fp)
{
perror ("The following error occurred");
return ;
}
fgets(line,len,fp);
printf("%s",line);
fclose(fp);
fp=fopen("/home/c-sandbox/index.html", "a");
if(!fp)
{
perror ("The following error occurred");
return ;
}
fprintf(fp, "Testing...\n");
fclose(fp)
}
for reading "hello, world" string present in file.
after reading write to the same file "Testing..."