I have a buffer and I want to read a pascal file and put content in the buffer. Then I want to add '$' sign in the end of buffer. When I tried to do it i get only the last row from my pascal file into buffer I don't why. please help. Here is my code!
FILE *fp = fopen("test.pas", "r");
while(!feof(fp)){
fscanf(fp, "%s", buffer);
}
strcat(buffer,"$"); fclose(fp);
You are reading the lines, the problem is that you are overwriting them over and over again in your buffer, so only the last one stays.
A good way to do this is to use fscanf in the while condition, this way you'll have a sound stop condition and you can verify the read results, which should allways be done.
You can do something like this:
Live demo
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LINES 100 //nr of lines
int main() {
//array of 100 pointers to char, so 100 lines max, adapt it to you needs
//should be the equal or larger than the max number of lines to be read
char *buffer[LINES];
FILE *fp;
int i = 0;
//checking the opened file is also a good practice
if (!(fp = fopen("test.pas", "r"))) {
perror("Not able to open file!");
return 1;
}
do {
if (!(buffer[i] = malloc(100))) { //allocate memory for each line
perror("Memory allocation failed"); //checking memory allocation
return 1;
}
}while (fscanf(fp, "%99s", buffer[i]) == 1 && strcat(buffer[i], "$") && i++ < LINES - 1);
buffer[i] = NULL; // sentinel, marks the end of the array of strings
i = 0; //reset i
while (buffer[i]) {
puts(buffer[i]); //print each line
free(buffer[i]); //free memory
i++;
}
fclose(fp);
}
Note that fscanf() reads until the next blank space, so for strings with more than 1 word you should use something like fgets or you if you use UNIX, getline().
feof is not the best option as you can see in
Why is “while ( !feof (file) )” always wrong?
The standard actually exemplifies the correct usage of feof ISO/IEC9899:2017 N2176 § 7.21.6.2 - 19
Related
there is very long "dict.txt" file.
the size of this file is about 2400273(calculated by fseek, SEEK_END)
this file has lots of char like this 'apple = 사과'(simillar to dictionary)
Main problem is that reading file takes very long time
I couldn't find any solution to solve this problem in GOOGLE
The reason i guessed is associated with using fgets() but i don't know exactly.
please help me
here is my code written by C
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
int line = 0;
char txt_str[50];
FILE* pFile;
pFile = fopen("dict_test.txt", "r");
if (pFile == NULL) {
printf("file doesn't exist or there is problem to open your file\n");
}
else {
do{
fgets(txt_str, 50, pFile);;
line++;
} while (txt_str != EOF);
}
printf("%d", line);
}
Output
couldn't see result because program was continuosly running
Expected
the number of lines of this txt file
Major
OP's code fail to test the return value of fgets(). Code needs to check the return value of fgets() to know when to stop. #A4L
do{
fgets(txt_str, 50, pFile);; // fgets() return value not used.
Other
Line count should not get incremented when fgets() returns NULL.
Line count should not get incremented when fgets() read a partial line. (I. e.) the line was 50 or longer. Reasonable to use a wider than 50 buffer.
Line count may exceed INT_MAX. There is always some upper bound, yet trivial to use a wider type.
Good practice to close the stream.
Another approach to count lines would use fread() to read chunks of memory and then look for start of lines. (Not shown)
Recommend to print a '\n' after the line count.
int main(void) {
FILE* pFile = fopen("dict_test.txt", "r");
if (pFile == NULL) {
printf("File doesn't exist or there is problem to open your file.\n");
return EXIT_FAILURE;
}
unsigned long long line = 0;
char txt_str[4096];
while (fgets(txt_str, sizeof txt_str, pFile)) {
if (strlen(txt_str) == sizeof txt_str - 1) { // Buffer full?
if (txt_str[sizeof txt_str - 1] != '\n') { // Last not \n?
continue;
}
}
line++;
}
fclose(pFile);
printf("%llu\n", line);
}
fgets returns NULL on EOF.
You are never assigning the result of
fgets(txt_str, 50, pFile);
to txt_str, your program never sees the end of the file and thus enters an endless loop.
try something like this:
char* p_str;
do{
p_str = fgets(txt_str, 50, pFile);
} while (p_str != NULL);
So I have the txt file from which I need to read the number of students written in that file, and because every student is in separate line, it means that I need to read the number of lines in that document. So I need to:
Print all lines from that document
Write the number of lines from that document.
So, I write this:
#include "stdafx.h"
#include <stdio.h>
int _tmain(int argc, _TCHAR* Argo[]){
FILE *student;
char brst[255];
student = fopen("student.txt", "r");
while(what kind of condition to put here?)
{
fgetc(brst, 255, (FILE*)student);
printf("%s\n", brst);
}
return 0;
}
Ok, I understand that I can use the same loop for printing and calculating the number of lines, but I can't find any working rule to end the loop. Every rule I tried caused an endless loop. I tried brst != EOF, brst != \0. So, it works fine and print all elements of the document fine, and then it start printing the last line of document without end. So any suggestions? I need to do this homework in C language, and I am using VS 2012 C++ compiler.
OP's code is close but needs to use fgets() rather than fgetc() and use the return value of fgets() to detect when to quit, it will be NULL #Weather Vane. Also add a line counter.
#include <stdio.h>
int main(void) {
FILE *student = fopen("student.txt", "r");
unsigned line_count = 0;
if (student) {
char brst[255];
// fgetc(brst, 255, (FILE*)student);
while (fgets(brst, sizeof brst, student)) {
line_count++;
printf("%u %s", line_count, brst);
}
fclose(student);
}
printf("Line Count %u\n", line_count);
return 0;
}
Try this:
#include "stdafx.h"
#include <stdio.h>
int _tmain(int argc, _TCHAR* Argo[]){
FILE *student;
char brst[255];
char* result = NULL;
//Ensure file open works, if it doesn't quit
if ((student = fopen("student.txt", "r")) == NULL)
{
printf("Failed to load file\n");
return 1;
}
//Read in the file
for ( (result = fgets( brst, sizeof(brst), student));
!feof(student);
(result = fgets( brst, sizeof(brst), student)) )
{
if ( result == NULL ) break; //I've worked on embedded systems where this actually ment waiting on data, not EOF, so a 'continue' would go here instead of break in that case
printf("%s\n", brst);
}
fclose( student );
return 0;
}
feof() is only true after you've read past the end of the file. Using a for with two identical reads, and feof() on the conditional is a simple way to ensure you read the file as expected.
Use feof() to check for an eof condition.
You are correctly reading the file line-by-line, but use fgets(), not fgetc() - and the cast is not needed.
Then use sscanf() to assign the line data to variables (or some "safe" form of it).
Here is my code but it is not making any output to console window. I need to print from output file and also wrap the lines for a particular number of characters, say, 20 character per line:
#include <stdio.h>
#define SIZE 100
int
main (int argc, char *argv[])
{
FILE *fp = NULL;
char line[SIZE] = { 0 };
int i = 0;
for (i = 0; i < argc; i++)
{
printf ("The argc %d is %s\n", i, argv[i]);
}
fp = fopen (argv[1], "r");
if (fp == NULL)
{
printf ("Can't open input file\n");
}
else
{
while (!feof (fp))
{
if (fgets (line, sizeof line, fp))
{
printf ("%s", line);
}
}
}
if (fclose (fp) != 0)
{
printf ("Error closing file\n");
}
return 0;
}
Your code makes no attempt to do line wrapping.
What you need to do (broadly speaking) is as follows:
Maintain a temporary buffer
Read each line of the file
If the line read is \n (only), output the buffer followed by \n, and go to 2.
If the buffer is empty, THEN replace the buffer by the line that is read ELSE append a space to the buffer and append the line read to the buffer.
If the buffer has more than 20 characters (if you are line wrapping on twenty characters), find the 20th character, and count backwards until you find a white space. Output the buffer up to that character with a \n, and replace the buffer by the data in the buffer after the whitespace.
At the end, output any remaining characters in the buffer followed by \n.
Implementing this is left as an exercise for the reader (we can't do all your homework for you).
Please also see #JoachimPileborg's wise advice re reading 'Why is while ( !feof (file) ) always wrong?'
this is my first question asked on here so if I'm not following the formatting rules here please forgive me. I am writing a program in C which requires me to read a few lines from a file. I am attempting to put each line into a cstring. I have declared a 2D character array called buf which is to hold each of the 5 lines from the file. The relevant code is shown below
#include <stdlib.h>
#include <sys/types.h>
#include <sys/file.h>
#include <sys/socket.h>
#include <sys/un.h> /* UNIX domain header */
void FillBuffersForSender();
char buf[5][2000]; //Buffer for 5 frames of output
int main()
{
FillBuffersForSender();
return 0;
}
void FillBuffersForSender(){
FILE *fp;
int line = 0;
char* temp = NULL;
size_t len = 0;
ssize_t read;
fp = fopen("frames.txt", "r");
printf("At the beginning of Fill Buffers loop.\n");
//while ((read = getline(&temp, &len, fp)) != -1){
while(line < 5){
//fprintf(stderr, "Read in: %s\n", temp);
fgets(temp, 2000, fp);
strcpy(buf[line], temp);
line++;
fprintf(stderr, "Line contains: %s.\n", temp);
temp = NULL;
}
while(line != 0){
fprintf(stderr, "Line contains: %s.\n", buf[line]);
line--;
}
}
The line
strcpy(buf[line], temp);
is causing a segmentation fault. I have tried this numerous ways, and cannot seem to get it to work. I am not used to C, but have been tasked with writing a bidirectional sliding window protocol in it. I keep having problems with super basic issues like this! If this were in C++, I'd be done already. Any help anyone could provide would be incredible. Thank you.
temp needs to point to an allocated buffer that fgets can write into.
In C programming, error checking is an important part of every program (in fact sometimes it seems like there's more error handling code than functional code). The code should check the return value from every function to make sure that it worked, e.g. if fopen returns NULL then it wasn't able to open the file, likewise if fgets returns NULL it wasn't able to read a line.
Also, the code needs to clean up after itself. For example, there is no destructor that closes a file when the file pointer goes out of scope, so the code needs to call fclose explicitly to close the file when it's finished with the file.
Finally, note that many of the C library functions have quirks that need to be understood, and properly handled. You can learn about these quirks by reading the man pages for the functions. For example, the fgets function will leave the newline character \n at the end of each line that it reads. But the last line of a file may not have a newline character. So when using fgets, it's good practice to strip the newline.
With all that in mind, the code should look like this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXLINE 5
#define MAXLENGTH 2000
static char buffer[MAXLINE][MAXLENGTH];
void FillBufferForSender(void)
{
char *filename = "frames.txt";
FILE *fp;
if ((fp = fopen(filename, "r")) == NULL)
{
printf("file '%s' does not exist\n", filename);
exit(1);
}
for (int i = 0; i < MAXLINE; i++)
{
// read a line
if (fgets( buffer[i], MAXLENGTH, fp ) == NULL)
{
printf("file does not have %d lines\n", MAXLINE);
exit(1);
}
// strip the newline, if any
size_t newline = strcspn(buffer[i], "\n");
buffer[i][newline] = '\0';
}
fclose(fp);
}
int main(void)
{
FillBufferForSender();
for (int i = 0; i < MAXLINE; i++)
printf("%s\n", buffer[i]);
}
Note: for an explanation of how strcspn is used to strip the newline, see this answer.
When it comes to C you have to think of the memory. Where is the memory for a point with NULL assigned to it? How can we copy something to somewhere that we have no space for?
I want to read the data of the file into a string.
Is there a function that reads the whole file into a character array?
I open the file like this:
FILE *fp;
for(i = 0; i < filesToRead; i++)
{
fp = fopen(name, "r");
// Read into a char array.
}
EDIT: So how to read it "line by line" getchar() ?
Here are three ways to read an entire file into a contiguous buffer:
Figure out the file length, then fread() the whole file. You can figure out the length with fseek() and ftell(), or you can use fstat() on POSIX systems. This will not work on sockets or pipes, it only works on regular files.
Read the file into a buffer which you dynamically expand as you read data using fread(). Typical implementations start with a "reasonable" buffer size and double it each time space is exhausted. This works on any kind of file.
On POSIX, use fstat() to get the file and then mmap() to put the entire file in your address space. This only works on regular files.
You can do the following:
FILE *fp;
int currentBufferSize;
for(i = 0; i < filesToRead; i++)
{
fp = fopen(name, "r");
currentBufferSize = 0;
while(fp != EOF)
fgets(filestring[i], BUFFER_SIZE, fp);
}
Of course you would have to make this in a more robust way, checking if your buffer can hold all the data and so on...
You might use something like the following: where you read each line, carefully check the result and pass it to a datastructure of your choosing. I have not shown how to properly allocate memory, but you can malloc up front and realloc when necessary.
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#define FILE_BUFFER_SIZE 1024
int file_read_line(FILE *fp, char *buffer)
{
// Read the line to buffer
if (fgets(buffer, FILE_BUFFER_SIZE, fp) == NULL)
return -errno;
// Check for End of File
if (feof(fp))
return 0;
return 1;
}
void file_read(FILE *fp)
{
int read;
char buffer[FILE_BUFFER_SIZE];
while (1) {
// Clear buffer for next line
buffer[0] = '\0';
// Read the next line with the appropriate read function
read = file_read_line(fp, buffer);
// file_read_line() returns only negative numbers when an error ocurred
if (read < 0) {
print_fatal_error("failed to read line: %s (%u)\n",
strerror(errno), errno);
exit(EXIT_FAILURE);
}
// Pass the read line `buffer` to whatever you want
// End of File reached
if (read == 0)
break;
}
return;
}