I have to read "N" int from .txt file and place each one to an array X[i]
But the problem is, I'm not suposed to know how many int are in the txt. The code has to work for every txt following this model
5 4
1 2 3
1 3 4
2 3 5
4 5 5
So I have, in the first line, the second number (4 in the exemple) the number of int in the txt will be N=4*3 (4 lines with 3 numbers (ALWAYS second number*3)) + 2 (first line)
The only code I know how to do is when I know how much numbers, like
int t[14] // I know there are 14 numbers on the .txt
while(fgets(buf, sizeof(buf), fp)) {
int result = sscanf(buf, "%d %d %d %d %d %d %d %d %d %d %d %d %d %d", &t[0], &t[1], &t[2], &t[3], &t[4], &t[5], &t[6],&t[7],&t[8],&t[9],&t[10], &t[11],&t[12],&t[13]);
if (result <= 0) break; // EOF, IO error, bad data
for (r=0; r<result; r++) {
if (i >= sizeof(X)/sizeof(X[0])) break; // too many
X[i++] = t[r]; //put them in the X[MAX]
}
}
And I need to read every number cause like in
2 3 5
I'll place 5 to a array[2][3]
How I am supposed to do this?
Can someone show me an example???
Thanks!
A simple template:
int a, b, i;
int *N;
if(fscanf(fp, "%d%d", &a, &b) != 2) { /* Read the first 2 integers */
/* Unable to read in 2 integers. Handle error... */
}
N = malloc(3 * b * sizeof(int)); /* Allocate enough space */
for(i = 0; i < 3*b; ++i) {
if(fscanf(fp, "%d", &N[i]) != 1) { /* Read numbers one-by-one */
/* Input may not be enough. Handle error... */
}
}
/* Now you have (3*b) integers stored in N */
/* after operations completed... */
free(N);
There is no need to read in line-by-line and guess how many numbers are there. Just call fscanf() again and again since your input is delimited by space characters and newline characters.
Related
I'm not sure why I'm receiving this error. I was wondering could it be due to my terminal not being able to read the txt files that run with this program. Let me know if that could be a possible reason for that message.
Im mainly just looking for syntax errors. The files I have just contain a big bunch of numbers and I'm supposed to work from the third value onwards {the first two have another use)
#include <stdlib.h>
#define N 1000000
int main(void)
{
int n; /* The number of lengths */
int x; /* The target length */
int lengths[N]; /* The array of available lengths */
int i, j;
int whichfile=1;
FILE *fp;
scanf("%d", &whichfile);
switch (whichfile) {
case 1:
fp = fopen("testcase_small_sorted.txt", "r");
break;
case 2:
fp = fopen("testcase_large_sorted.txt", "r");
break;
case 3:
fp = fopen("testcase_small_nomatch_sorted.txt","r");
break;
case 4:
fp = fopen("hidden_small_sorted.txt","r");
break;
case 5:
fp = fopen("hidden_large_sorted.txt","r");
break;
}
fscanf(fp, "%d", &x);
fscanf(fp, "%d", &n);
for (i=0;i<n;i++)
fscanf(fp, "%d", &lengths[i]);
fclose(fp);
/* Now all the input data has been read in
search for the required pair of lengths... */
x = lengths[0];
n = lengths[1];
for(i = 2; i < n; i++)
{
for(j = 2; i < n; j++)
{
if(lengths[i] + lengths[j] == x)
{
printf("Found: %d + %d == %d\n", lengths[i], lengths[j], x);
}
}
}
return 0;
} ```
I'm mainly just looking for syntax errors.
Syntax errors are only the beginning. C will not check anything for you. You have to check if files opened, if input scans worked, if values are inside array bounds. If you don't, that's how you get segfaults.
For files, the usual pattern is to try to open the file, check its return value, and then handle the error. fopen returns NULL on error and sets errno. errno is a global which holds what sort of error happened like "file not found", but it's a number. strerror is handy to turn it into an error message. Finally fprintf is like printf but can print to things other than stdout. In this case stderr. Both stdout and stderr normally appear on the screen, but they can be separated.
FILE *fp = fopen(path, mode);
if( fp == NULL ) {
// This will print something like "Could not open testcase_small_sorted.txt: No such file or directory"
fprintf(stderr, "Could not open file %s: %s", path, strerror(errno));
exit(1);
}
But now we need to copy this five times because the code repeats fopen. Instead of each case opening the file, what if it just picked a filename? And since each filename has a number, what if they were just in an array?
const char *files[] = {
NULL, // 0 is not used
"testcase_small_sorted.txt",
"testcase_large_sorted.txt",
"testcase_small_nomatch_sorted.txt",
"hidden_small_sorted.txt",
"hidden_large_sorted.txt"
};
const char *path = files[whichfile];
What if they input something that's not a number? Or what if the number is out of range? These need to be checked for as well. scanf will return the number of items matched. We expect 1. If we get anything else it didn't work.
// Check that we read an integer.
if( scanf("%d", &whichfile) != 1 ) {
fprintf(stderr, "Please enter 1-5.\n");
exit(1);
}
// Check that it's in range.
if( (whichfile < 1) || (5 < whichfile) ) {
fprintf(stderr, "Please enter 1-5.\n");
exit(1);
}
Note that scanf has a lot of problems and should be swiftly discarded once you learn things like fgets and sscanf.
int lengths[1000000] is 4 to 8 megabytes (1 million integers at 4 or likely 8 bytes per integer) and might get you an eponymous stack overflow. Your algorithm is O(n^2) which means if there really were 1,000,000 items it would take 1,000,000,000,000 iterations to find all the pairings and your class will probably be done before the program is.
(A little hint to improve the algorithm: if the numbers are sorted, and you're looking for two of them to sum X, do you need to check every number?)
I think you're meant trust n from the file for how many to read. Normally you don't have this, it's a crutch to let you read input without using dynamic memory (you'll be taught that later). Even if you had it, you wouldn't trust it anyway in production code; if it lies you'll walk out of your array bounds. But for this exercise that's fine.
// Read the first two lines, the sum and the number of remaining lines.
// Note that `fscanf` can also fail and needs to be error checked.
// I'll leave that as an exercise.
fscanf(fp, "%d", &x);
fscanf(fp, "%d", &n);
// Use `n` to allocate just enough space on the stack.
int lengths[n];
// Read the rest.
// Use braces, even for one line.
// They avoid a very silly and hard to debug mistake.
for (i=0;i<n;i++) {
fscanf(fp, "%d", &lengths[i]);
}
fclose(fp);
There's no need to put x and n into lengths. They aren't meant to be summed and you skip over them anyway by starting your loops at 2.
With that fixed the loops can start at 0. There is a mistake in the inner loop, it should check j < n not i < n.
for(i = 0; i < n; i++)
{
for(j = 0; j < n; j++) // <<--- j < n, not i < n.
{
if(lengths[i] + lengths[j] == x)
{
printf("Found: %d + %d == %d\n", lengths[i], lengths[j], x);
}
}
}
My C Code is as so:
#include <stdio.h>
int main( int argc, char ** argv){
FILE *myFile;
myFile = fopen("numbers.txt", "r");
//read file into array
int numberArray[16];
for (int i = 0; i < 16; i++){
fscanf(myFile, "%1d", &numberArray[i]);
}
for (int i = 0; i < 16; i++){
printf("Number is: %d\n", numberArray[i]);
}
}
My numbers.txt file contains the follow values:
5
6
70
80
50
43
But for some reason my output
Number is: 5
Number is: 6
Number is: 7
Number is: 0
Number is: 8
Number is: 0
Number is: 5
Number is: 0
Number is: 4
Number is: 3
Number is: 0
Number is: 0
Number is: 4195904
Number is: 0
Number is: 4195520
Number is: 0
However I'm expecting it to print out numberArray to print out the identical contents of the text file. I'm not exactly sure why it's doing this, does anyone happen to know the reason? I'm aware that I'm making an array bigger than the amount of values that I can store, but I'm still confused as to why it can't store 70, 80, etc into one index?
It is because you are reading only 1 digit at a time.
Hence change the below.
fscanf(myFile, "%1d", &numberArray[i]);
to
fscanf(myFile, "%d", &numberArray[i]);
And your array should be of size number of integers in the file.
int numberArray[6];
for (int i = 0; i < 6; i++)
or
while (fscanf(myFile, "%d", &numberArray[i++]) == 1);
#include <stdio.h>
#include <stdlib.h>
int main(void) {
FILE *myFile = fopen("numbers.txt", "r"); // just init your variable directly
if (!myFile) { // Always check if there is no error
return EXIT_FAILURE; // handle it as you like
}
#define SIZE 16 // Avoid magic number
int numberArray[SIZE];
size_t n = 0; // n will represent the size of valid values inside the array
// Always check if scanf family has parsed your input also "%1d" ask to only parse
// one digit, so use %d if you want parse an integer
while (n < SIZE && fscanf(myFile, "%d", numberArray + n) == 1) {
n++;
}
for (size_t i = 0; i < n; i++) {
printf("Number is: %d\n", numberArray[i]);
}
}
I found an answer to the first part of my question (how to read multiple values with scanf) but it doesn't seem to work for me (I think it's because of putting the values into an array and maybe also because I'm checking if the values given are 6 ints for sure):
I am writing a program that stores co-ordinates of 4 triangles in an array. Each line has 6 values and stores co-ordinates of one triangle. I want to read 6 co-ordinates at one time and do this operation for 4 triangles separately.
int tab[4][6];
for (int i = 0; i < 4; i++){
while (scanf("%d %d %d %d %d %d", &tab[i][0], &tab[i][1], &tab[i][2], &tab[i][3], &tab[i][4], &tab[i][5]) != 6){
printf("Error, try again: ");
while (getchar() != '\n'){}
}
}
So for example if first triangle's co-ordinates are (2,1), (5,6), (2,7), then I want to type in: "2 1 5 6 2 7" and as a result I want it to fill the first line of the array with the said numbers in the order I typed them in.
Obviously it doesn't work, the program stops working (not finishes the work, it stops) after the first line is given.
I get this error after debugging (after giving first line):
"Unhandled exception at 0x0FDCC28C (msvcr120d.dll) in xxx.exe: 0xC0000005: Access violation writing location 0xCCCCCCCC."
How to fix it?
You need to subtract the pointer i when detecting input error like this for example ->
#include <stdio.h>
int main(int argc, const char * argv[]) {
int tab[4][6];
for (int i = 0; i < 4; i++){
printf("Enter 6 values \n");
int retVal=scanf("%d %d %d %d %d %d", &tab[i][0], &tab[i][1], &tab[i][2], &tab[i][3], &tab[i][4], &tab[i][5]);
if (retVal == 6) {
printf("You did enter -> %d %d %d %d %d %d\n",tab[i][0],tab[i][1],tab[i][2],tab[i][3],tab[i][4],tab[i][5]);
} else {
printf("Error entering values.. (Enter numbers). \n");
while (getchar() != '\n'){}
i--;
}
}
return 0;
}
Unclear why OP's code failed without posting input used and prior code.
How to fix it?
Use fgets() to read a line of user input. Avoid mixing scanf() with fgets() in prior code. Then parse the buffer. Use " %n" at the end to look for success and extra text.
int tab[4][6];
char buf[6*12 * 2]; // Use a buffer twice expected max needs
for (int i = 0; i < 4; i++) {
while (1) {
if (fgets(buf, size buf, stdin) == NULL) {
return "Failed to read enough data"; // Handle end-of-file in some fashion
}
int n = 0;
sscanf(buf, "%d%d%d%d%d%d %n",
&tab[i][0], &tab[i][1], &tab[i][2], &tab[i][3], &tab[i][4], &tab[i][5], &n);
if (n > 0 && buf[n] == 0) {
break; // Success!
}
printf("Error - bad input, try again: ");
}
}
#include<stdlib.h>
#include<stdio.h>
int main() {
FILE* file = fopen ("fourth.txt", "r");
int i = 0;
int rows=0;
int rows2=0;
int columns=0;
int counter=0;
int length=0;
int multiply=0;
fscanf (file, "%d", &i);
rows=i;
printf("the rows are %d\n", i);
int matrix[rows][rows];
length=rows*rows;
if (rows<=0) {
printf("error, this file cannot be processed");
return 0;
}
do
{
if (fscanf(file, "%d", &i)==1) {
if (counter<length) {
matrix[rows2][columns]=i;
counter++;
columns++;
if (columns==rows) {
rows2++;
columns=0;
}
}
multiply=i;
}
} while (!feof(file));
fclose (file);
for ( int c = 0; c < rows; c++ ) {
for ( int j = 0; j < rows; j++ ) {
printf("matrix[%d][%d] = %d\n", c,j, matrix[c][j] );
}
}
printf("the multiply is %d", multiply);
I am trying to create a matrix exponential (matrix multiplication in another words). However before I perform the actual mathematical process, I have to read numbers as input from a txt file and store them in a 2d array. Above is what I have from the code so far, however, I am struggling to actually input the numbers into the array because when I was testing my 2d array out at the very end, I was getting odd results.
for example:
1. Inputs:
3
123
456
789
2
The 3 represents the number of rows, which is the same as the number of columns for this particular 2d array because the matrix is square, meaning
all rows and columns are the same.
The 2 represents the exponent, which is the number of times I have to multiply the original matrix by itself.
However my output is
matrix[0][0] = 123
matrix[0][1] = 456,
matrix[0][2] = 789
matrix[1][0] = 2
matrix[1][1] = 4214800
matrix[1][2] = 0
matrix[2][0] = 3
matrix[2][1] = 0
matrix[2][2] = 0
Expected output has to be:
123
456
789
in a 2d array
Is there a reason why?
Also how would I modify the code so no matter what the input is in the txt file regarding different rows and columns, I could still format the proper 2d array. Thanks
In your input text file, the digits in a line are not separated in any way. If you need multi-digit numbers, consider separating them by a symbol like space or semicolon.
If the matrix has only single digit whole numbers (ie, numbers from 0 to 9), it would be fine.
But if there the 3 numbers in a line are, say, 21, 13 and 4, in the input file it would be just 21134.
There's no way to find if it was 211,3,4 or 21,1,34 or 2,113,4 or .......
With the fscanf() in your program, each %d will read the entire line considering it to be a single number and assign it to the variable i.
Instead of reading the size first into i and then copying it to rows like
fscanf (file, "%d", &i);
rows=i;
you could directly read into rows
fscanf( file, "%d", &rows);
And read the values like
for(rows2=0; rows2<rows; ++rows2)
{
if( fscanf(file, "%1d%1d%1d", &matrix[rows2][0], &matrix[rows2][1], &matrix[rows2][2]) != 3)
{
perror("Error");
break;
}
}
Then read the value for multiply at the end like
fscanf(file, "%d", &multiply);
You may check the return value of fscanf() to check if any error occurred.
You used !feof(file) to check end of file. I don't know much but have a look here.
I'm a programming noob so please bear with me.
I'm trying to read numbers from a text file into an array. The text file, "somenumbers.txt" simply holds 16 numbers as so "5623125698541159".
#include <stdio.h>
main()
{
FILE *myFile;
myFile = fopen("somenumbers.txt", "r");
//read file into array
int numberArray[16];
int i;
for (i = 0; i < 16; i++)
{
fscanf(myFile, "%d", &numberArray[i]);
}
for (i = 0; i < 16; i++)
{
printf("Number is: %d\n\n", numberArray[i]);
}
}
The program doesn't work. It compiles but outputs:
Number is: -104204697
Number is: 0
Number is: 4200704
Number is: 2686672
Number is: 2686728
Number is: 2686916
Number is: 2004716757
Number is: 1321049414
Number is: -2
Number is: 2004619618
Number is: 2004966340
Number is: 4200704
Number is: 2686868
Number is: 4200798
Number is: 4200704
Number is: 8727656
Process returned 20 (0x14) execution time : 0.118 s
Press any key to continue.
change to
fscanf(myFile, "%1d", &numberArray[i]);
5623125698541159 is treated as a single number (out of range of int on most architecture). You need to write numbers in your file as
5 6 2 3 1 2 5 6 9 8 5 4 1 1 5 9
for 16 numbers.
If your file has input
5,6,2,3,1,2,5,6,9,8,5,4,1,1,5,9
then change %d specifier in your fscanf to %d,.
fscanf(myFile, "%d,", &numberArray[i] );
Here is your full code after few modifications:
#include <stdio.h>
#include <stdlib.h>
int main(){
FILE *myFile;
myFile = fopen("somenumbers.txt", "r");
//read file into array
int numberArray[16];
int i;
if (myFile == NULL){
printf("Error Reading File\n");
exit (0);
}
for (i = 0; i < 16; i++){
fscanf(myFile, "%d,", &numberArray[i] );
}
for (i = 0; i < 16; i++){
printf("Number is: %d\n\n", numberArray[i]);
}
fclose(myFile);
return 0;
}
for (i = 0; i < 16; i++)
{
fscanf(myFile, "%d", &numberArray[i]);
}
This is attempting to read the whole string, "5623125698541159" into &numArray[0]. You need spaces between the numbers:
5 6 2 3 ...
Loop with %c to read the stream character by character instead of %d.
There are two problems in your code:
the return value of scanf must be checked
the %d conversion does not take overflows into account (blindly applying *10 + newdigit for each consecutive numeric character)
The first value you got (-104204697) is equals to 5623125698541159 modulo 2^32; it is thus the result of an overflow (if int where 64 bits wide, no overflow would happen). The next values are uninitialized (garbage from the stack) and thus unpredictable.
The code you need could be (similar to the answer of BLUEPIXY above, with the illustration how to check the return value of scanf, the number of items successfully matched):
#include <stdio.h>
int main(int argc, char *argv[]) {
int i, j;
short unsigned digitArray[16];
i = 0;
while (
i != sizeof(digitArray) / sizeof(digitArray[0])
&& 1 == scanf("%1hu", digitArray + i)
) {
i++;
}
for (j = 0; j != i; j++) {
printf("%hu\n", digitArray[j]);
}
return 0;
}
enter your file input like this
ex:
12
13
22
45
(after every number hit enter)
then run your programm it will run properly