Reading in bytes of a file for printable ASCII characetrs - c

Question

I have to write a program that takes a file name from the command line.
It then read several bytes from the file, looking for strings of printable characters (ASCII values between 32 and 126 decimal).
Then print out the strings.
A string is a run of at least 4 consecutive printable characters and ends whenever a non-printable character is encountered.
Whenever such a string is found, print it out on a new line.
What I have so far is:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]){
FILE *fp;
fp = fopen(argv[1], "rb");
char buffer;
while(fp != NULL)
{
fread(&buffer, 1, 1, fp);
}
fclose(fp);
}
What I think this does it take the program from the command line and read in all the bytes of the file 1 by 1 and store them into buffer.
Now I need to check each part of the array and see if each element is between 32 and 136.
If it is, I add those bytes to another array until there is a byte not in this range.
Do this for the entirety of the buffer array.
Is this a code approach and is this right so far?

Answer 1

Change the while loop a bit. What you're checking is whether the file exits or not in a loop which won't fetch the required result you want.
fp is comapared with NULL to find out if the file opening is succesful or not as fopen returns address of the file if it opens a file or NULL saying something went wrong.
if( fp == NULL )
{
perror("Error while opening the file\n");
exit(0);
}
What you want do is following lines:
while( ( ch = fgetc(fp) ) != EOF ) { // reads character by character from the file
if((ch <32) || (ch>136)) // check if it is in range to printed
break;
else
printf("%c",ch); // format whoever you want
}

Answer 2

If I understand you correctly, you want your program to read characters from a file (the file might contain non-printable characters), and check if the character falls in the range of 32 to 126 (printable character). If it is, then add that character to a buffer and read more characters until a non-printable character is found. It should also make sure that the string should have at least 4 characters; string should be printed on a newline.
Here is the code that might help you. It was compiled with gcc, and I hope it works for you too.
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
FILE *fp;
char buf[100], ch; //the size of the array would vary according to your need
int i=0;
//check for enough arguments
if(argc<2)
{
printf("\nInsufficient Arguments.\n");
printf("\nUsage: PrintChar <file>\n\n");
return 1;
}
//open the file in binary mode and check for exisitence of the file
if((fp = fopen(argv[1], "rb"))== NULL)
{
printf("\nError: Unable to open the file.\n");
return 2;
}
i=0;
while( (ch = fgetc(fp))!=EOF )
{
//check for the range
if(ch>=32 && ch<=126)
{
buf[i] = ch; i++;
//This loop will run till it find a next unprintable character (not between the range of 32 and 126
//we also check for the EOF while reading the characters
while( ( (ch = fgetc(fp))>=32 && ch<=126 ) && ch!=EOF )
{
buf[i] = ch; i++;
}
buf[i] = '\0'; //adding the NULL character
//if the string is at least of 4 letters, print it
if(i>=4)
printf("\n%s", buf);
//reset the counter
i=0;
}
}
fclose(fp);
return 0;
}
File contents - test.txt, that I used:
---------------------------------------------------------------
This is a string
anotherline of text #$%#$%#$% #$% #$%345#$$%&$&##$!##~#######
!∞▬345345µ∞#452353453$%##$%#$%$%%^&%^*4234346443754754451} 
and this is the output of the program:
C:\Users\shine\Documents\MYCPROGS\forStackoverflow>printchar test.txt
This is a string
anotherline of text #$%#$%#$% #$% #$%345#$$%&$&##$!##~#######
345#$%##$%##452353453$%##$%#$%$%%^&%^*4234346443754754451}
345345
-------------------------------------------------------------------
Hope this would be helpful. I made this is a hurry, so please let me know if you find something wrong in it.

Answer 3

Read one character each time, write when we find long enough string or have to:
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
size_t min_str_len = 4;
size_t buf_len = 4; /* Must greater than or equal to min_str_len */
char buf[buf_len], ch;
size_t out_len, last_len;
last_len = out_len = 0;
while (fread(&ch, 1, 1, stdin) > 0) {
if (isprint(ch)) {
buf[out_len++] = ch;
if (out_len >= buf_len) {
fwrite(buf, 1, out_len, stdout);
last_len += out_len;
out_len = 0;
}
}
else {
if (out_len + last_len >= min_str_len) {
fwrite(buf, 1, out_len, stdout);
#ifdef NEWLINE
fwrite("\n", 1, 1, stdout);
#endif
last_len = out_len = 0;
}
else {
out_len = 0;
}
}
}
exit(EXIT_SUCCESS);
}
If you want to read more than one byte each time, this "at least 4 consecutive printable characters" will make it a little bit tricky:
#include <assert.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
size_t str_min_len = 4;
size_t buf_len = 1024; /* Must greater than or equal to str_min_len */
char in_buf[buf_len], out_buf[buf_len];
size_t out_len, in_len, last_len;
last_len = out_len = 0;
while ((in_len = fread(in_buf, 1, buf_len, stdin)) > 0) {
assert(out_len == 0);
for (size_t i = 0; i < in_len; i++) {
char ch = in_buf[i];
if (isprint(ch)) {
out_buf[out_len++] = ch;
}
else {
if (out_len + last_len >= str_min_len) {
fwrite(out_buf, 1, out_len, stdout);
#ifdef NEWLINE
/* Write a newline between strings. */
fwrite("\n", 1, 1, stdout);
#endif
last_len = 0;
}
out_len = 0;
}
}
if (0 < out_len && out_len < str_min_len) {
size_t pad_len = str_min_len - out_len;
for (size_t i = 0; i < pad_len; i++) {
char ch;
if (fread(&ch, 1, 1, stdin) < 1) {
exit(EXIT_SUCCESS);
}
else if (isprint(ch)) {
out_buf[out_len++] = ch;
}
else {
break;
}
}
}
if (out_len >= str_min_len) {
fwrite(out_buf, 1, out_len, stdout);
last_len = out_len;
out_len = 0;
}
else {
last_len = out_len = 0;
}
}
exit(EXIT_SUCCESS);
}