I wanted to learn how to use getc function in C so I wrote a little program that is supposed to give the first letter of a text file as an output.
Here's how it looks:
int main()
{
int character;
FILE *file;
file = fopen("file.txt", "r");
if(file == NULL)
printf("can't open\n");
character = getc(file);
printf("%c", character);
fclose(file);
return 0;
}
It fails to open the file.txt file and I can't figure out why. file.txt is in the same folder as my program's .exe file. I'm using Windows Vista.
Thanks in advance
This extracts the program's location from argv[0]
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MYFILE "plik.txt"
int main(int argc, char *argv[]) {
char fname[_MAX_PATH+1];
int znak;
FILE *plik;
char *ptr;
strcpy(fname, argv[0]);
ptr = strrchr(fname, '\\');
if(ptr == NULL) {
strcpy(fname, MYFILE);
}
else {
strcpy(ptr+1, MYFILE);
}
plik = fopen(fname, "r");
if(plik == NULL) {
printf("Can't open %s\n", fname);
}
else {
znak = getc(plik);
printf("First char of %s is %c\n", fname, znak);
fclose(plik);
}
getchar();
return 0;
}
Try
if (plik == NULL) { perror("plik.txt"); exit(EXIT_FAILURE); }
for a better understanding of the cause of error.
Related
I am trying to figure out why this is not printing, I am trying to print each letter from a text file that is inputted through command prompt, but I am just getting an empty output... What am I doing wrong, and why does this not work? I feel like this logically should work. Thanks.
int main(int argc, char *argv[]) {
FILE *fp;
int i;
for (i = 1; i < argc; i++) {
printf("%s\n", argv[i]);
fp = fopen(argv[i], "r");
while (!feof(fp)) {
puts(fp);
}
fclose(fp);
}
return 0;
}
You are attempting to print a file pointer:
puts(fp);
Read the manual of puts() -that's not what it takes.
To read char-by-char and print on the stdout, you can do:
int ch;
fp = fopen(argv[i], "r");
if (!fp) {
perror("fopen");
exit(1);
}
while((ch=fgetc(fp)) != EOF) {
putchar(ch);
}
flcose(fp);
Unless you are passing multiple file names as arguments, your outer loop doesn't make much sense.
Your program has multiple problems:
You do not test the return value of fopen(): the program invokes undefined behavior if any of the command line arguments cannot be opened as a stream for reading.
while(!feof(fp)) is incorrect. Read this: Why is “while ( !feof (file) )” always wrong?
puts(fp); is incorrect as fp is a FILE *, not a string. Use a loop to copy the file contents one byte at a time.
Here is a corrected version:
#include <errno.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[]) {
FILE *fp;
int i, c;
for (i = 1; i < argc; i++) {
fp = fopen(argv[i], "r");
if (fp == NULL) {
fprintf(stderr, "cannot open %s: %s\n", argv[i], strerror(errno));
} else {
printf("%s\n", argv[i]);
while ((c = getc(fp)) != EOF) {
putchar(c);
}
fclose(fp);
}
}
return 0;
}
int main(int argc, char *argv[]) {
FILE *fp;
int i;
char buff[128];
for (i = 1; i < argc; i++) {
printf("\n%s\n", argv[i]);
if(NULL == (fp = fopen(argv[i], "r"))){//check open file
perror("fopen");
continue;
}
while (fgets(buff, sizeof buff, fp)) {//read into buffer
fputs(buff, stdout);//print buffer (not add newline)
}
fclose(fp);
}
return 0;
}
I wrote this code to read a variable in a .txt file, ignore the first character and convert into a integer.It works but looks dumb, is there a better way to do this? I'm using just one string here but it's supposed to work with four.
void read(char a[])
{
int i;
char a1[3];
for (i = 0; i<3; ++i){
a1[i]= a[i+1];
}
int b1 = atoi(a1);
}
int main()
{
FILE *file;
file = fopen( "file.txt", "r");
if (file == NULL) {
printf( "Arquivo nao encontrado\n");
}
char a[4];
fscanf(file, "%s\n",&a);
read(a);
return 0;
}
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
const char filename[] = "file.txt";
FILE *fp = fopen(filename, "r");
if (fp == 0)
{
fprintf(stderr, "Failed to open file %s for reading\n", filename);
return(EXIT_FAILURE);
}
int value;
if (fscanf(fp, "%*c%d", &value) != 1)
{
fprintf(stderr, "Failed to read integer value from file %s\n", filename);
fclose(fp);
return EXIT_FAILURE;
}
printf("Read %d\n", value);
fclose(fp);
return 0;
}
The %*c reads a single character but does not assign it. The * to suppress an assignment is a general mechanism in the scanf()
family of functions.
Untested code.
How to redirect more than one text file in c program? For example I have the following C code:
//redirection.c
#include<stdio.h>
main()
{
int x,y;
scanf("%d",&x);
x=x*x;
printf("%d",x);
scanf("%d",&y);
y=x+y;
printf("%d",y);
}
After compiling this code I created two text files text1.txt having the value 8 and text2.txt having the value 6.
When I give input to this program using command line redirection (as redirection<text1.txt), it gives output 64 and does not wait to take another input (and program exits) which I want to give another input from text2.txt.
Is there any solution how can I send another input via text2.txt for second scanf function in the above program?
While giving the input as redirection as like this.
cat a b | ./a.out.
Or else you can use the command line arguments.
#include<stdio.h>
main(int argc, char *argv[])
{
FILE *fp, *fp1;
if ( (fp=fopen(argv[1],"r")) == NULL ){
printf("file cannot be opened\n");
return 1;
}
if (( fp1=fopen(argv[2],"r")) == NULL ){
printf("file cannot be opened\n");
return 1;
}
int x,y;
fscanf(fp,"%d",&x);// If you having only the value in that file
x=x*x;
printf("%d\n",x);
fscanf(fp1,"%d",&y);// If you having only the value in that file
y=x+y;
printf("%d\n",y);
}
you can also use command line arguments:
#include <stdio.h>
#define BUFSIZE 1000
int main(int argc, char *argv[])
{
FILE *fp1 = NULL, *fp2 = NULL;
char buff1[BUFSIZE], buff2[BUFSIZE];
fp1 = fopen(argv[1], "r");
while (fgets(buff1, BUFSIZE - 1, fp1) != NULL)
{
printf("%s\n", buff1);
}
fclose(fp1);
fp2 = fopen(argv[2], "r");
while (fgets(buff2, BUFSIZE - 1, fp2) != NULL)
{
printf("%s\n", buff2);
}
fclose(fp2);
}
here is a more cleaned up version:
#include <stdio.h>
#define BUFSIZE 1000
void print_content(char *file);
int main(int argc, char *argv[])
{
print_content(argv[1]);
print_content(argv[2]);
}
void print_content(char *file){
char buff[BUFSIZE];
FILE *fp = fopen(file, "r");
while (fgets(buff, sizeof(buff), fp) != NULL)
{
printf("%s\n", buff);
}
fclose(fp);
}
I am new to programming and have a few questions as to how to implement this idea.
I am looking to have a user enter their name/string of digits and if their name is on a list, to then execute a string of commands. I am not to sure how to impliment this, but with some gogle-ing I was able to come up with this code:
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char userName[10];
printf("\n\n\n\nPlease enter your name: ");
scanf_s("%s",userName); // userName should be verified/found inside the results.dat file
FILE *fp;
fp = fopen("results.dat", "r");
if (fp == NULL) {
printf("I couldn't open results.dat for writing.\n");
exit(0);
}
if (fp == John) {
//Dispence squence of pills for John
}
if (fp == Mary) {
//Dispence squence of pills for Mary
}
return 0;
}
I do not think I am using the if statement correctly. how can I do something like:
if (content in fp == john, execute/call another function)
Thanks in advance!
Try this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
char userName[10];
char names[20];
printf("\n\n\n\nPlease enter your name: ");
scanf("%s",userName); // userName should be verified/found inside the results.dat file
FILE *fp;
fp = fopen("results.dat", "r");
if (fp == NULL) {
printf("I couldn't open results.dat for writing.\n");
exit(0);
}
while(fgets(names, 20, fp)) // fgets reads a line from the file
{
names[strlen(names)-1] = '\0'; // but it leaves the newline character "\n" , so the strings won't match
if(strcmp(names, userName) == 0) // if the value returned by strcmp is zero then string match
{
printf("Match found\n");
}
}
return 0;
}
fopen simply opens a file for reading and/or writing, to read the actual content of the file you need to use functions such as fgets, fscanf and so on.
Short example
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char* argv[])
{
char name[64];
char buffer[64];
printf ("Please enter your name: ");
file = fopen ("results.dat", "rw");
if (!file) {
printf ("Results.dat could not be opened.\n");
exit(-1);
}
if ( fgets (buffer, 64, file)) {
if (strcmp (buffer, "john")) {
printf ("Contents of file is john\n");
}
}
return 0;
}
1) I'm trying to open a file, read the mix data (ints, chars and strings) and store them into args.
1.1) so in the sample.txt is a total of 13 (excluding args[0])
2) Need to read a file from terminal "./myprog.c < sample.txt"
Heres my code and have no idea where i went wrong:
sample.txt:
123 213 110 90 1
hello my friend
boo bleh
a b c
myprog.c:
#include <stdio.h>
int main()
{
int i = 1;
FILE *fstin=fopen(argv[0], "r"); //open the file
if (fstin == NULL) {
puts("Couldn't fopen...");
return -1;
}
//Getting all the inputs from file
while ((fscanf(fstin, "%d", argv[i])) != EOF){
i++;
}
fclose(fstin);
for (i=0; i<10; i++) {
printf("%d\n",argv[i]);
}
return 0;
}
Any help is greatly appreciated!
PS: Would like if anyone could post their complete solution? Will upload unto this post and let everyone have a review of this problem
PPS: Please excuse the poor level of coding as I am a beginner and completely new to C.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int ac, char *av[]){
int i, argc=0;
char **argv=NULL, data[16];
FILE *fstin = stdin;
if(ac == 2){
if(NULL==(fstin = fopen(av[1], "r"))){
puts("Couldn't fopen...");
return -1;
}
}
while (1==fscanf(fstin, "%15s", data)){
argv = realloc(argv, (argc+1)*sizeof(char*));
argv[argc] = malloc(strlen(data)+1);
strcpy(argv[argc++], data);
}
if(ac == 2)
fclose(fstin);
for (i=0; i<argc; ++i) {
printf("%s\n", argv[i]);
}
//deallocate
return 0;
}
You are making mistake at 2nd point where you divert your file to other file which is wrong. Actually you need to first compile and need to make executable.
gcc -o my_prog ./myprog.c -Wall
You need to execute this program as below to read file from c program:
./my_prog ./sample.txt
As you are new to C programming first go to man pages related to file operations.
Solution:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[]) {
//If command line argument is not inserted then stop operation
if (2 != argc) {
printf("Invalid number of arguments : %d\n", argc);
return -1;
}
int size = 0, ret = 0;
char *data = NULL;
FILE *fp = NULL;
//Open file in read mode given from command line argument
if (NULL != (fp = fopen(argv[1], "r")))
{
//Find size of file
fseek(fp, 0L, SEEK_END);
size = ftell(fp);
fseek(fp, 0L, SEEK_SET);
//if file is empty no need to read it.
if (size > 0)
{
//Data pointer which contains file information
data = (char *) calloc(sizeof(char), size);
if (NULL != data)
{
//Read whole file in one statement
fread(data, sizeof(char), size, fp);
printf("File %s is readed successfully\n", argv[1]);
printf("Data:\n");
printf("%s\n", data);
free(data); data = NULL;
}
else
{
perror("memory allocation failed\n");
ret = -1;
}
}
else
{
printf("File %s is empty\n", argv[1]);
}
fclose(fp); fp = NULL;
}
else
{
perror("File open failed\n");
ret = -1;
}
return ret;
}
Now Test it on your setup and if any query please post comments.