Im trying to read a text file with inputs in the above format. Im able to read each line with this code:
FILE *file = fopen(argv[1], "r");
...
char * line = NULL;
size_t len = 0;
ssize_t read;
while ((read = getline(&line, &len, file)) != -1)
so that "line" is equal to each line in the file and if i output what is read for ex: i get the first output as "1 2 3 4 5 6 7 8 9". How can i store these numbers to a 2d array ?. how can i split at each space and get the number only ?
Sample using sscanf
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char *argv[]) {
int numbers[9][9];
FILE *file = fopen(argv[1], "r");
char * line = NULL;
size_t len = 0;
ssize_t read;
int rows = 0;
while ((read = getline(&line, &len, file)) != -1){
int *a = numbers[rows];
if(9 != sscanf(line, "%d%d%d%d%d%d%d%d%d", a, a+1, a+2,a+3,a+4,a+5,a+6,a+7,a+8)){
fprintf(stderr, "%s invalid format at input file\n", line);
return EXIT_FAILURE;
}
if(++rows == 9)
break;
}
fclose(file);
free(line);
//check print
for(int r = 0; r < 9; ++r){
for(int c = 0; c < 9; ++c)
printf("%d ", numbers[r][c]);
puts("");
}
}
A string is an array, so you just want to copy the contents of the string, character by character to another array, unless the character is not alphanumeric.
You could do some checks first to see how many alphanumeric characters are in the current string and then grab that amount of memory for your new array.
Related
I need help to read the numbers of a .txt file and put them in an array. But only from the second line onwards. I'm stuck and don't know where to go from the code that i built.
Example of the .txt file:
10 20
45000000
48000000
56000000
#define MAX 50
int main (void){
FILE *file;
int primNum;
int secNum;
int listOfNumers[50];
int numberOfLines = MAX;
int i = 0;
file = fopen("file.txt", "rt");
if (file == NULL)
{
printf("Error\n");
return 1;
}
fscanf(file, "%d %d\n", &primNum, &secNum);
printf("\n1st Number: %d",primNum);
printf("\n2nd Number: %d",secNum);
printf("List of Numbers");
for(i=0;i<numberOfLines;i++){
//Count the number from the second line onwards
}
fclose(file);
return 0;
}
You just need a loop to keep reading ints from file and populate the listOfNumers array until reading an int fails.
Since you don't know how many ints there are in the file, you could also allocate the memory dynamically. Example:
#include <stdio.h>
#include <stdlib.h>
int main(void) {
FILE* file = fopen("file.txt", "rt");
if(file == NULL) {
perror("file.txt");
return 1;
}
int primNum;
int secNum;
if(fscanf(file, "%d %d", &primNum, &secNum) != 2) {
fprintf(stderr, "failed reading primNum and secNum\n");
return 1;
}
unsigned numberOfLines = 0;
// allocate space for one `int`
int* listOfNumers = malloc((numberOfLines + 1) * sizeof *listOfNumers);
// the above could just be:
// int* listOfNumers = malloc(sizeof *listOfNumers);
while(fscanf(file, "%d", listOfNumers + numberOfLines) == 1) {
++numberOfLines;
// increase the allocated space by the sizeof 1 int
int* np = realloc(listOfNumers, (numberOfLines + 1) * sizeof *np);
if(np == NULL) break; // if allocating more space failed, break out
listOfNumers = np; // save the new pointer
}
fclose(file);
puts("List of Numbers:");
for(unsigned i = 0; i < numberOfLines; ++i) {
printf("%d\n", listOfNumers[i]);
}
free(listOfNumers); // free the dynamically allocated space
}
There are a few ways to approach this; if you know the size of the first line, you should be able to use fseek to move the position of the file than use getline to get each line of the file:
int fseek(FILE *stream, long offset, int whence);
The whence parameter can be:
SEEK_SET : the Beginning
SEEK_CUR : the current position
SEEK_END : the End
The other option would to encapsulate the entire file read in a while loop:
char *line = NULL;
size_t linecap = 0;
ssize_t linelen;
int counter = 0;
while((linelen = getline(&line, &linecap, file)) != -1){
if counter == 0{
sscanf(line, "%d %d\n", &primNum, &secNum);
}else{
//Process your line
}
counter++; //This would give you your total line length
}
Hi I was trying to create an array of string of an undetermined length in c.
This is my code :
int main()
{
int lineCount=linesCount();
char text[lineCount][10];
printf("%d",lineCount);
FILE * fpointer = fopen("test.txt","r");
fgets(text,10,fpointer);
fclose(fpointer);
printf("%s",text);
return 0;
}
I would like to replace 10 in
char text[lineCount][10];
My code reads out a file I already made the amount of lines dynamic.
Since the line length is unpredictable I would like to replace 10 by a something dynamic.
Thanks in advance.
To do this cleanly, we want a char * array rather than an 2D char array:
char *text[lineCount];
And, we need to use memory from the heap to store the individual lines.
Also, don't "hardwire" so called "magic" numbers like 10. Use an enum or #define (e.g) #define MAXWID 10. Note that with the solution below, we obviate the need for using the magic number at all.
Also, note the use of sizeof(buf) below instead of a magic number.
And, we want [separate] loops when reading and printing.
Anyway, here's the refactored code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
linesCount(void)
{
return 23;
}
int
main(void)
{
int lineCount = linesCount();
char *text[lineCount];
char buf[10000];
printf("%d", lineCount);
// open file and _check_ the return
const char *file = "test.txt";
FILE *fpointer = fopen(file, "r");
if (fpointer == NULL) {
perror(file);
exit(1);
}
int i = 0;
while (fgets(buf, sizeof(buf), fpointer) != NULL) {
// strip newline
buf[strcspn(buf,"\n")] = 0;
// store line -- we must allocate this
text[i++] = strdup(buf);
}
fclose(fpointer);
for (i = 0; i < lineCount; ++i)
printf("%s\n", text[i]);
return 0;
}
UPDATE:
The above code is derived from your original code. But, it assumes that the linesCount function can predict the number of lines. And, it doesn't check against overflow of the fixed length text array.
Here is a more generalized version that will allow an arbitrary number of lines with varying line lengths:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
main(void)
{
int lineCount = 0;
char **text = NULL;
char buf[10000];
// open file and _check_ the return
const char *file = "test.txt";
FILE *fpointer = fopen(file, "r");
if (fpointer == NULL) {
perror(file);
exit(1);
}
int i = 0;
while (fgets(buf, sizeof(buf), fpointer) != NULL) {
// strip newline
buf[strcspn(buf,"\n")] = 0;
++lineCount;
// increase number of lines in array
text = realloc(text,sizeof(*text) * lineCount);
if (text == NULL) {
perror("realloc");
exit(1);
}
// store line -- we must allocate this
text[lineCount - 1] = strdup(buf);
}
fclose(fpointer);
// print the lines
for (i = 0; i < lineCount; ++i)
printf("%s\n", text[i]);
// more processing ...
// free the lines
for (i = 0; i < lineCount; ++i)
free(text[i]);
// free the list of lines
free(text);
return 0;
}
Here, I am trying to read from a text file, copy this file into an array, then I want to write the array to another text file. This is not copying into the array at all. I am just getting blank values when I print.
int main(void)
{
char char_array[50];
char copied_array[50];
//int n = 2;
FILE* fpointer = fopen("hello_world.txt", "r");
FILE* fpointer2 = fopen("copyhello.txt", "w");
for(int i = 0;i < 50; i++)
{
fread(&char_array, sizeof(char), 1, fpointer);
copied_array[i] = char_array[i];
}
for(int j = 0;j < 50; j++)
{
printf("char_array: %c\n", copied_array[j]);
}
fclose(fpointer);
fclose(fpointer2);
}
working code. hope this becomes clearer :)
Note you're using fread/fwrite - compare with fgets/fputs for strings.
#include "stdio.h"
#include "string.h"
#define BUFSIZE 50
// memory size 'plus one' to leave room for a string-terminating '\0'
#define BUFMEMSIZE (BUFSIZE+1)
const char *file1 = "hello_world.txt";
const char *file2 = "copyhello.txt";
int main(void)
{
char char_array[BUFMEMSIZE];
char copied_array[BUFMEMSIZE];
FILE *fInput, *fOutput;
fInput = fopen(file1, "r");
if(fInput != NULL)
{
fOutput = fopen(file2, "w");
if(fOutput != NULL)
{
// make sure memory is wiped before use
memset(char_array, 0, BUFMEMSIZE);
memset(copied_array, 0, BUFMEMSIZE);
size_t lastSuccessfulRead = 0;
// the read-then-loop pattern: try and read 50 chars
size_t bytesRead = fread(char_array, sizeof(char), BUFSIZE, fInput);
while(bytesRead != 0)
{
// we got at least 1 char ..
// (to be used at end - so we know where in char_array is the last byte read)
lastSuccessfulRead = bytesRead;
// 'bytesRead' bytes were read : copy to other array
strncpy(copied_array, char_array, bytesRead);
// write to output file, number of bytes read
fwrite(copied_array, sizeof(char), bytesRead, fOutput);
// read more, and loop, see if we got any more chars
bytesRead = fread(char_array, sizeof(char), BUFSIZE, fInput);
}
// set char after the last-read-in char to null, as a string-terminator.
char_array[lastSuccessfulRead] = '\0';
// an array of chars is also a 'string'
printf("char_array: %s\n", char_array);
fclose(fOutput);
}
else printf("cant open %s\n", file2);
fclose(fInput);
}
else printf("cant open %s\n", file1);
}
Supposing that I have two files like this:
file1.txt
john
is
the new
guy
file2.txt
man
the old
is
rick
cat
dog
I'd like to compare first line from file1 with all the lines from file2 and verify if it exist. If not, go two the second line from file1 and compare it with all the lines from file2.. and so on until eof is reached by file1.
The output that I expect is:
john
the new
guy
How I thought this should be done:
read file1 and file2
create a function which returns the line number of each of them
take the first line from file1 and compare it to all the lines from file2
do this until all the lines from file1 are wasted
Now, I don't know what I'm doing wrong, but I don't get the result that I expect:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int countlines(char *filename)
{
int ch = 0, lines = 0;
FILE *fp = fopen(filename, "r");
if (fp == NULL)
return 0;
do {
ch = fgetc(fp);
if (ch == '\n')
lines++;
} while (ch != EOF);
if (ch != '\n' && lines != 0)
lines++;
fclose(fp);
return lines;
}
int main(int argc, char *argv[])
{
FILE *template_file = fopen(argv[1], "r");
FILE *data_file = fopen(argv[2], "r");
char buffer_line_template_file[100];
char buffer_line_data_file[100];
if (argc != 3)
{
perror("You didn't insert all the arguments!\n\n");
exit(EXIT_FAILURE);
}
if (template_file == NULL || data_file == NULL)
{
perror("Error while opening the file!\n\n");
exit(EXIT_FAILURE);
}
int counter = 0;
for (int i = 0; i < countlines(argv[1]); i++)
{
fgets(buffer_line_template_file, 100, template_file);
for (int j = 0; j < countlines(argv[2]); j++)
{
fgets(buffer_line_data_file, 100, data_file);
if (strcmp(buffer_line_template_file, buffer_line_data_file) != 0)
{
counter++;
printf("%d", counter);
}
}
}
printf("\n\n");
return 0;
}
Could someone please point me into the right direction ? For testing purposes I created a counter at the end which was a part of a small debug. There should be the print() function
As per #chux answer I got the following simplified code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
FILE *template_file = fopen(argv[1], "r");
FILE *data_file = fopen(argv[2], "r");
char buffer_line_template_file[100];
char buffer_line_data_file[100];
if (argc != 3)
{
perror("You didn't insert all the arguments!\n\n");
exit(EXIT_FAILURE);
}
if (template_file == NULL || data_file == NULL)
{
perror("Error while opening the file!\n\n");
exit(EXIT_FAILURE);
}
while(fgets(buffer_line_template_file, 100, template_file))
{
buffer_line_template_file[strcspn(buffer_line_template_file, "\n")] = '\0';
rewind(data_file);
while (fgets(buffer_line_data_file, 100, data_file))
{
buffer_line_data_file[strcspn(buffer_line_data_file, "\n")] = '\0';
if (strcmp(buffer_line_template_file, buffer_line_data_file) != 0)
{
printf("%s\n", buffer_line_template_file);
}
}
}
printf("\n\n");
return 0;
}
The above code is giving me the following output, which is not what is expected:
john
john
john
john
john
john
is
is
is
is
is
the new
the new
the new
the new
the new
the new
guy
guy
guy
guy
guy
guy
Problems with OP's code
Imprecise definition of line.
Excessive recalculation
Fuzzy determination of the number of lines in a file.
Unlike string, which has a precise definition in C, reading a line is not so well defined. The primary specificity issue: does a line contain the trailing '\n'. If the first answer is Yes, then does the last text in a file after a '\n' constitute a line? (Excessively long lines are another issue, but let us not deal with that today.)
Thus possibly some lines end with '\n' and others do not, fooling strcmp("dog", "dog\n").
The easiest solution is to read a line until either 1) a '\n' is encountered, 2) EOF occurs or 3) line buffer is full. Then after getting a line, lop off the potential trailing '\n'.
Now all lines code subsequently works with have no '\n'.
fgets(buffer_line_template_file, 100, template_file);
buffer_line_template_file[strcspn(buffer_line_template_file, "\n")] = '\0';
OP's loop is incredible wasteful. Consider a file with 1000 lines. Code will loop, calling 1000 times countlines() (each countlines() call reads 1000 lines) times when one countlines() call would suffice.
// for (int j = 0; j < countlines(argv[2]); j++)
int j_limit = countlines(argv[2]);
for (int j = 0; j < j_limit; j++)
There really is no need to count the line anyways, just continue until EOF (fgets() returns NULL). So no need to fix its fuzzy definition. (fuzzy-ness concerns same issues as #1)
int counter = 0;
for (fgets(buffer_line_template_file, 100, template_file)) {
buffer_line_template_file[strcspn(buffer_line_template_file, "\n")] = '\0';
rewind(data_file);
while ((fgets(buffer_line_data_file, 100, data_file)) {
buffer_line_data_file[strcspn(buffer_line_data_file, "\n")] = '\0';
if (strcmp(buffer_line_template_file, buffer_line_data_file) != 0) {
counter++;
printf("%d", counter);
}
}
}
Other simplifications possible - for another day.
FWIW, following counts lines of text allowing the last line in the file to optionally end with a '\n'.
unsigned long long FileLineCount(FILE *istream) {
unsigned long long LineCount = 0;
rewind(istream);
int previous = '\n';
int ch;
while ((ch = fgetc(inf)) != EOF) {
if (previous == '\n') LineCount++;
previous = ch;
}
return LineCount;
}
Note that this function may get a different result that fgets() calls. Consider a file of one line of 150 characters. fgets(..., 100,...) will report 2 lines. FileLineCount() reports 1.
[Edit] Updated code to conform to OP functionality.
int found = 0;
while (fgets(buffer_line_data_file, 100, data_file))
{
buffer_line_data_file[strcspn(buffer_line_data_file, "\n")] = '\0';
if (strcmp(buffer_line_template_file, buffer_line_data_file) == 0)
{
found = 1;
break;
}
}
if (!found) printf("%s\n", buffer_line_template_file);
This program prints the diff of two files file1.txt and file2.txt.
#include<stdio.h>
#include <stdlib.h>
#include <memory.h>
int main() {
FILE *fp1, *fp2;
int ch1, ch2;
char fname1[40], fname2[40];
char *line = NULL;
size_t len = 0;
ssize_t read;
char *line2 = NULL;
size_t len2 = 0;
ssize_t read2;
fp1 = fopen("file1.txt", "r");
fp2 = fopen("file2.txt", "r");
if (fp1 == NULL) {
printf("Cannot open %s for reading ", fname1);
exit(1);
} else if (fp2 == NULL) {
printf("Cannot open %s for reading ", fname2);
exit(1);
} else {
while ((read = getline(&line, &len, fp1)) != -1 && (read2 = getline(&line2, &len2, fp2)) != -1) {
if (!strcmp(line, line2)) {
printf("Retrieved diff on line %zu :\n", read);
printf("%s", line);
}
}
if (ch1 == ch2)
printf("Files are identical \n");
else if (ch1 != ch2)
printf("Files are Not identical \n");
fclose(fp1);
fclose(fp2);
}
return (0);
}
You already have a very good answer (and always will from chux), but here is a slightly different approach to the problem. It uses automatic storage to reading file2 into an array of strings and then compares each line in file1 against every line in file2 to determine whether it is unique. You can easily convert the code to dynamically allocate memory, but for sake of complexity that was omitted:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
enum { MAXC = 256, MAXL = 512 };
void file1infile2 (FILE *fp2, FILE *fp1, size_t *n2, size_t *n1);
int main (int argc, char **argv) {
FILE *fp1 = fopen (argc > 1 ? argv[1] : "file1.txt", "r");
FILE *fp2 = fopen (argc > 2 ? argv[2] : "file2.txt", "r");
size_t n1 = 0, n2 = 0;
if (!fp1 || !fp2) {
fprintf (stderr, "error: file open failed.\n");
return 1;
}
printf ("\nunique words in file1, not in file 2.\n\n");
file1infile2 (fp2, fp1, &n2, &n1);
printf ("\nanalyzed %zu lines in file1 against %zu lines in file2.\n\n",
n1, n2);
return 0;
}
void file1infile2 (FILE *fp2, FILE *fp1, size_t *n2, size_t *n1)
{
char buf[MAXC] = "";
char f2buf[MAXL][MAXC] = { "" };
size_t i;
*n1 = *n2 = 0;
while (*n2 < MAXL && fgets (buf, MAXC, fp2)) {
char *np = 0;
if (!(np = strchr (buf, '\n'))) {
fprintf (stderr, "error: line exceeds MAXC chars.\n");
exit (EXIT_FAILURE);
}
*np = 0;
strcpy (f2buf[(*n2)++], buf);
}
while (*n1 < MAXL && fgets (buf, MAXC, fp1)) {
char *np = 0;
if (!(np = strchr (buf, '\n'))) {
fprintf (stderr, "error: line exceeds MAXC chars.\n");
exit (EXIT_FAILURE);
}
*np = 0, (*n1)++;
for (i = 0; i < *n2; i++)
if (!(strcmp (f2buf[i], buf)))
goto matched;
printf (" %s\n", buf);
matched:;
}
}
Look over the code and let me know if you have any questions.
Example Use/Output
$ ./bin/f1inf2 dat/f1 dat/f2
unique words in file1, not in file 2.
john
the new
guy
analyzed 4 lines in file1 against 6 lines in file2.
I'm trying to read the number of a txt file like this:
input=20
output=10
hidden=5
....
I tried with this code:
char line[30];
char values[100][20];
int i = 0;
FILE *fp;
fp = fopen("myFile.txt", "r");
if(fp == NULL)
{
printf("cannot open file\n");
return 0;
}
while(fgets(line, sizeof(line), fp) != NULL)
{
sscanf(line, "%[^=]", values[i])
printf("%s\n", values[i]);
i++;
}
fclose(fp);
But I obtain only the first word and never the number after the =.
I get
input
output
etc
instead of
20
10
5
etc
How can I get the number??
This line
sscanf(line, "%[^=]", values[i]);
means "read everything up to, but not including, the = sign into values[i]".
If you are interested in the numeric part after the equal sign, change the call as follows:
sscanf(line, "%*[^=]=%19s", values[i]);
This format line means "read and ignore (because of the asterisk) everything up to, and including, the equal sign. Then read a string of length of up to 19 characters into values[i]".
Demo.
Don't use sscanf() for that, redeclare values to store the integers like
int values[LARGE_CONSTANT_NUMBER];
and after fgets() just use strchr
char *number;
number = strchr(line, '=');
if (number == NULL)
continue;
number += 1;
values[i] = strtol(number, NULL, 10);
you could also use malloc() and realloc() if you wish, to make the values array dynamic.
Try it if you like
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(void)
{
char line[100];
int values[100];
int i;
FILE *fp;
size_t maxIntegers;
fp = fopen("myFile.txt", "r");
if (fp == NULL)
{
perror("cannot open file\n");
return 0;
}
i = 0;
maxIntegers = sizeof(values) / sizeof(values[0]);
while ((fgets(line, sizeof(line), fp) != NULL) && (i < maxIntegers))
{
char *number;
number = strchr(line, '=');
if (number == NULL) /* this line does not contain a `=' */
continue;
values[i++] = strtol(number + 1, NULL, 10);
printf("%d\n", values[i - 1]);
}
fclose(fp);
return 0;
}
with this technique you avoid unecessarily storing the number as a string.