I can't figure out why this isn't working.
#include <stdio.h>
int main(void) {
FILE *in, *out;
// char *FULLPATH = "C:\\Users\\Jay\\c\\workspace\\I-OFiles\\in.txt\\ ";
// char *mode = "r";
// in = fopen(FULLPATH, mode);
//
// if (in == NULL) {
// perror("Can't open in file for some reason\n");
// exit (1);
// }
out = fopen("C:\\Users\\Jay\\c\\workspace\\I-OFiles\\out.txt", "w");
if (out == NULL) {
perror("Can't open output file for some reason \n");
exit(1);
}
fprintf(out, "foo U");
fclose(in);
fclose(out);
return 0;
}
if I remove the // from the commented lines, the error compiler gives is
: Invalid argument
I don't understand why (I read all the other threads related, and nothing).
It does actually write the out.txt file OK, so it doesn't seem like a path misspelled problem.
Remove backslash after in.txt.
The input file name seems bogus:
"C:\\Users\\Jay\\c\\workspace\\I-OFiles\\in.txt\\ "
The filename is just a single space " " and in.txt is probably not a directory.
Change the code to:
const char *FULLPATH = "C:\\Users\\Jay\\c\\workspace\\I-OFiles\\in.txt";
Or preferably:
const char *FULLPATH = "C:/Users/Jay/c/workspace/I-OFiles/in.txt";
for better portability as forward slashes work in Windows as well as in Unix.
Furthermore, it is easy to provide more information as to why fopen() failed to open the files.
Here is a modified version:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void) {
FILE *in, *out;
in = fopen("C:/Users/Jay/c/workspace/I-OFiles/in.txt", "r");
if (in == NULL) {
perror("Cannot open input file");
exit(1);
}
out = fopen("C:/Users/Jay/c/workspace/I-OFiles/out.txt", "w");
if (out == NULL) {
fclose(in);
perror("Cannot open output file");
exit(1);
}
fprintf(out, "foo U");
fclose(in);
fclose(out);
return 0;
}
Change backslash to slash.
Maybe you don't have permissions or something like that.
out = fopen("C://Users//Jay//c//workspace//I-OFiles//out.txt", "w");
if (!out)
perror("fopen");
return 0;
Related
I am unable to save a char array using fprint() and i cannot figure out why. The below codes compliles correctly but saves nothing to file. Please advise.
static char bitSpecial[100];
int main(int argc, char *argv[]) {
FILE *fp
fp = fopen(thefilename, "w+");
if (fp == NULL) {
printf("I couldn't open file for writing.\n");
exit(0);
}
/* populate bitSpecial one character at the time and verify array is full */
fprintf(fp,"%s", bitSpecial);
if (fclose(fp) != 0) puts("Unable to close the file");
return
}
It'll be easier to identify the problem with the full code. I tried the following snippet and it worked:
#include <stdio.h>
#include <string.h> // for strerror
#include <errno.h> // for errno
static char bitSpecial[100];
int main(int argc, char *argv[])
{
char * thefilename = "test";
FILE *fp;
fp = fopen(thefilename, "w+");
if (fp == NULL) {
printf("I couldn't open file for writing.\n");
return 1;
}
/* populate bitSpecial one character at the time and verify array is full */
bitSpecial[0] = 'a';
bitSpecial[1] = '\n';
bitSpecial[2] = '\0'; // terminator
if (fprintf(fp,"%s", bitSpecial) < 0)
printf("[+] fprintf failed with '%s'\n", strerror(errno));
if (fclose(fp) != 0)
puts("Unable to close the file");
return 0;
}
Verify that you put a null terminator (\0) at the end of bitSpecial, and check the return value of fprintf.
I want to read all files that I can find in the folder where my executable is, except the runnable file that I'm running. I code the following code but, although this list correctly the files that I have in my folder, I cannot open them with fopen because fopen prints that the file doesn't exists. If I do gedit "path of the file obtained from my program in c" then it opens perfectly from the term. Where is the bug?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <unistd.h>
int main (int argc, char **argv) {
//Determining the number of files we have.
//We call to a bash command http://stackoverflow.com/questions/646241/c-run-a-system-command-and-get-output
FILE *fp, *fin;
char path[1035], cwd[1024];
int scanned = 0;
/* Open the command for reading. */
//https://askubuntu.com/questions/370697/how-to-count-number-of-files-in-a-directory-but-not-recursively
//This count soft and hard links also (I think)
fp = popen("ls -F |grep -v /", "r");
if (fp == NULL) {
printf("Failed to run command\n" );
exit(1);
}
/* Read the output a line at a time - output it. */
//Loop for each file. Be careful! if the exe is inside, it will also be counted!
while (fgets(path, sizeof(path)-1, fp) != NULL) {
printf("Reading file: %s\n", path);
fin=fopen(path,"r");
scanned = 0;
printf("caa");
if (fin != NULL){
printf("AA\n");
fclose(fin);
}
if (!fin)perror("fopen");
printf("Done! \n");
}
/* close */
pclose(fp);
printf("end");
return 0;
}
There are 2 bugs in your code:
when the code updates the "path" variable in your code. It has a newline at the end which needs to be corrected to NUL. This gives an incorrect path.
Something like below can be appended to your code:
while (fgets(path, sizeof(path)-1, fp) != NULL) {
len=strlen(path);
path[len-1]='\0';
Use 'ls -A1', since 'ls -F' adds a '*' in binary name:
fp = popen("ls -A1 |grep -v /", "r");
ok so just in case someone else needs a better approach, I redid the code with the comments I had. Here I let you the new code.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <dirent.h>
#include <sys/types.h>
#include <sys/stat.h>
int isDirectory(const char *path) {
struct stat statbuf;
if (stat(path, &statbuf) != 0)
return 0;
return S_ISDIR(statbuf.st_mode);
}
int main (int argc, char **argv) {
FILE *fp, *fin;
char path[1035], cwd[1024];
int scanned = 0;
int ints;
DIR *dir;
struct dirent *ent;
//getcwd prints directory where the app ran.
if ((dir = opendir (getcwd(cwd, sizeof(cwd)))) != NULL) {
/* print all the files and directories within directory */
while ((ent = readdir (dir)) != NULL) {
/*Skips . and ..*/
if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0) continue;
if (isDirectory(ent->d_name) != 0) continue;
printf ("Reading file: %s\n", ent->d_name);
scanned = 0;
fin=fopen(ent->d_name,"r");
if (fin != NULL){
while ((scanned = fscanf(fin, "%d", ints)) != EOF) {
if(scanned == 1){
printf("%d\n", ints);
}else {
printf("Whoops! Input format is incorrect!\n");
break;
}
} //LOOP: reading file
fclose(fin);
}
if (!fin)perror("fopen");
printf("Done! \n");
}//LOOP: while opendir
closedir (dir);
} else {
/* could not open directory */
perror ("opendir");
return EXIT_FAILURE;
}
return 0;
}
I'm writing code that's supposed to verify that a .txt file is a certain format.
I wrote my code as I saw in a tutorial and in the website
and for some reason my program doesn't even print my file.
Can you tell me what I'm doing wrong?
The code will do something far more complex, but I'm still trying to work on my basics.
Here's my code so far:
int main(int argc, char *argv[]) {
/* argv[0] = name of my running file
* argv[1] = the first file that i receive
*/
define MAXBUFLEN 4096
char source[MAXBUFLEN + 1];
int badReturnValue = 1;
char *error = "Error! trying to open the file ";
if (argc != 2) {
printf("please supply a file \n");
return badReturnValue;
}
char *fileName = argv[1];
FILE *fp = fopen(argv[1], "r"); /* "r" = open for reading */
if (fp != NULL) {
size_t newLen = fread(&source, sizeof(char), MAXBUFLEN, fp);
if (ferror(fp) != 0) {
printf("%s %s", error, fileName);
return badReturnValue;
}
int symbol;
while ((symbol = getc(fp)) != EOF) {
putchar(symbol);
}
printf("finish");
fclose(fp);
}
else {
printf("%s %s", error, fileName);
return badReturnValue;
}
}
I think you need a bit more explanations:
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
// there might be a macro BUFLEN defined in stdio
// which size is optimized for reading in chunks.
// Test if avaiable otherwise define it
#ifndef BUFLEN
# define BUFLEN 4096
#endif
int main(int argc, char *argv[])
{
char source[BUFLEN];
char *filename;
FILE *fp;
size_t fpread, written;
char c;
int ret_fclose;
if (argc != 2) {
fprintf(stderr, "Usage: %s filename\n", argv[0]);
exit(EXIT_FAILURE);
}
// reset errno, just in case
errno = 0;
// work on copy
filename = malloc(strlen(argv[1]) + 1);
if (filename == NULL) {
fprintf(stderr, "Allocating %zu bytes failed\n", strlen(argv[1]) + 1);
exit(EXIT_FAILURE);
}
filename = strcpy(filename, argv[1]);
// try to open the file at 'filename'
fp = fopen(filename, "r");
if (fp == NULL) {
fprintf(stderr, "Opening file \"%s\" filename failed\n", filename);
// errno might got set to something usable, check and print
if (errno != 0) {
fprintf(stderr, "Error: %s\n", strerror(errno));
}
exit(EXIT_FAILURE);
}
// You have two options here. One is to read in chunks of MAXBUFLEN
while ((fpread = fread(&source, 1, BUFLEN, fp)) > 0) {
// Do something with the stuff we read into "source"
// we do nothing with it here, we just write to stdout
written = fwrite(&source, 1, fpread, stdout);
// you can use 'written' for error check when writing to an actual file
// but it is unlikely (but not impossible!) with stdout
// test if we wrote what we read
if ((fpread - written) != 0) {
fprintf(stderr, "We did not write what we read. Diff: %d\n",
(int) (fpread - written));
}
}
// fread() does not distinguish between EOF and error, we have to check by hand
if (feof(fp)) {
// we have read all, exit
puts("\n\n\tfinish\n");
// No, wait, we want to do it again in a different way, so: no exit
// exit(EXIT_SUCCESS);
} else {
// some error may have occured, check
if (ferror(fp)) {
fprintf(stderr, "Something bad happend while reading \"%s\"\n", filename);
if (errno != 0) {
fprintf(stderr, "Error: %s\n", strerror(errno));
}
exit(EXIT_FAILURE);
}
}
// the other way is to read it byte by byte
// reset the filepointers/errors et al.
rewind(fp);
// rewind() should have reseted errno, but better be safe than sorry
errno = 0;
printf("\n\n\tread and print \"%s\" again\n\n\n\n", filename);
// read one byte and print it until end of file
while ((c = fgetc(fp)) != EOF) {
// just print. Gathering them into "source" is left as an exercise
fputc(c, stdout);
}
// clean up
errno = 0;
ret_fclose = fclose(fp);
// even fclose() might fail
if (ret_fclose == EOF) {
fprintf(stderr, "Something bad happend while closing \"%s\"\n", filename);
if (errno != 0) {
fprintf(stderr, "Error: %s\n", strerror(errno));
}
exit(EXIT_FAILURE);
}
// The macros EXIT_FAILURE and EXIT_SUCCESS are set to the correct values for
// the OS to tell it if we had an eror or not.
// Using exit() is noot necessary here but there exits teh function atexit()
// that runs a given function (e.g: clean up, safe content etc.) when called
exit(EXIT_SUCCESS);
}
You read from the file twice but only print once.
If the file is to small the first reading will read all of the contents, and the second reading will not produce anything so you don't print anything.
I believe you have to reset the pointer after using fread.
Try fseek(fp, SEEK_SET, 0) to reset the pointer to the beginning of the file. Then print the file.
Here is a simple program that should copy the content of one
file named copyme into a file here. I have created copyme with a little text in it by the following commands:
touch copyme.txt
open copyme.txt
Then I typed in text, and saved the file with
touch copyme.txt command.
Then I compiled a program:
// Program to copy one file ot another
#include <stdio.h>
int main (void)
{
char in_name[64], out_name[64];
FILE *in, *out;
int c;
// get file names from user
printf("Enter name of file to be copied: ");
scanf("%63s", in_name);
printf("Entere name of output file: ");
scanf("%63s", out_name);
// open input and output files
if ( (in = fopen(in_name, "r")) == NULL)
{
printf("Can't open %s for reading.\n", in_name);
return 1;
}
if ( (out = fopen(out_name, "w")) == NULL)
{
printf("Can't open %s for writing.\n", out_name);
return 2;
}
while ((c = getc(in)) != EOF)
putc(c, out);
// Close open files
fclose (in);
fclose (out);
printf("File has been copied\n");
return 0;
}
And ran it in terminal.
Here is the output:
Enter name of file to be copied: copyme
Entere name of output file: here
Can't open copyme for reading.
The compiler doesn't recognize copyme file, although it is
physically exists in the folder (I see it, I open it, I read
it).
I would be grateful for help. I am new to this things.
Thank you!
change
if ( (in = fopen(in_name, "r")) == NULL)
{
printf("Can't open %s for reading.\n", in_name);
return 1;
}
to
#include <errno.h>
if ( (in = fopen(in_name, "r")) == NULL)
{
perror("Can't open file for reading.\n");
return 1;
}
you will get a human readable message telling you why it cant read the file
I'm playing with file I/O in C.. I'm trying to use fgets to read data in from one file and output it to another file. The problem is that it always returns NULL and so nothing gets copied to the output file. Here's my code:
#include <stdio.h>
#include <stdlib.h>
int main()
{
FILE *fpIn;
FILE *fpOut;
if ((fpIn = fopen("C:\\testIn.txt", "r") == NULL))
{
printf("Cannot open input file!\n");
exit(1);
}
if ((fpOut = fopen("C:\\testOut.txt", "a") == NULL))
{
printf("Cannot open output file!\n");
exit(1);
}
char buffer[128];
while (fgets(buffer, 128, fpIn) != NULL)
{
fputs(buffer, fpOut);
}
fclose(fpIn);
fclose(fpOut);
system("PAUSE");
return 0;
}
another thing; when I tried using "a+f" in the second arg for fopen, it didn't work.
if ((fpOut = fopen("C:\\testOut.txt", "a") == NULL))
Should be
if ((fpOut = fopen("C:\\testOut.txt", "a")) == NULL)
Same on the input file.
If you are new to C, I'd suggest do one thing at a time to make it easier to track down issues.
e.g.
fpOut = fopen("C:\\testOut.txt", "a");
if(fpOut == NULL) {
...