I am working on a project in C which requires me to read in matrix values from a txt file. The first two lines are the number of rows and columns, and the rest is the actual matrix data.
For example, something like this:
2
2
1.0 2.0
3.0 4.0
The code I wrote is giving me some issues. Here's a snippet:
matrix read(char* file){
FILE *fp;
printf("check 1\n");
fp = fopen(file,"r");
printf("file opened\n");
// Make the new matrix
matrix result;
printf("matrix created\n");
int counter = 0;
int i;
int j;
int holdRows;
int holdColumns;
if(counter == 0)
{ // read in rows
fscanf(fp, "%li", holdRows);
printf("here is holdRows: %li\n", holdRows);
counter++;
}
if(counter == 1)
{ // read in columns
fscanf(fp, "%li", holdColumns);
printf("here is holdColumns: %li\n", holdColumns);
counter++;
// Now that I know the dimensions, make the matrix
result = newMatrix(holdRows, holdColumns);
}
// For the rest, read in the values
for(i = 0; i < holdRows; i++)
for(j = 0; j < holdColumns; j++)
fscanf(fp, "%lf", &result->matrixData[i][j]);
fclose(fp);
return result;
}
Whenever I run this, holdRows and holdColumns are not the values stored in the txt file. For example, I tried a 3X4 matrix, and it read that there was one row and three columns.
Can anyone tell me what I'm doing wrong?
Thanks :)
Thanks to suggestions by you all and some sleuth work myself, I solved my problem. First, I was entering the wrong filename (well, now I feel silly), and second, I was reading the data in as the wrong type.
Thanks, everyone, for your help!
You are not passing the address of holdRows and holdColumns to fscanf. You have to change them to fscanf(fp, "%li", &holdRows); and fscanf(fp, "%li", &holdColumns);.
the %li conversion specification requires a long* as matching argument to fscanf(): you're passing a int (int* after correction proposed by dbarbosa).
Try "%i" ... and same for printf().
The %lf expects a double. Is matrix made of doubles?
Try replacing:
for(i = 0; i < holdRows; i++)
for(j = 0; j < holdColumns; j++)
fscanf(fp, "%lf", &result->matrixData[i][j]);
with
double temp;
for(i = 0; i < holdRows; i++)
for(j = 0; j < holdColumns; j++) {
fscanf(fp, "%lf", &temp);
result->matrixData[i][j] = temp;
}
I seem to recall that in C some types of 2D arrays don't play nice with &.
Related
It seems like I didn't quite understand how the file stream works. My text file right now contains the following integers: 1 10 5 4 2 3 -6, but I would like the program to be able to read any number of integers from the file, should it change.
Apparently I'm not even using the correct functions.
The code I have written is the following:
int main() {
printf("This program stores numbers from numeri.txt into an array.\n\n");
int a[100];
int num;
int count = 0;
FILE* numeri = fopen("numeri.txt", "r");
while (!feof(numeri)) {
num = getw(numeri);
a[count] = num;
if (fgetc(numeri) != ' ')
count++;
}
int i;
for (i = 0; i < count; i++) { printf("%d ", a[i]); }
return 0;
}
I would like it to print out the array with the stored numbers, but all I get is: 540287029 757084960 -1
Can someone help me understand what I did wrong and maybe tell me how to write this kind of code properly?
I have fixed your code based on comments. I used fscanf to read from file and limited the amount of numbers that can be stored in array by checking count < 100 and checking whether fscanf filled exactly one argument.
Also, I checked that whether file could be opened or not, just for safety. If it couldn't be opened, then just print error message and return 1.
int main() {
printf("This program stores numbers from numeri.txt into an array.\n\n");
int a[100] = {0};
int num;
int count = 0;
int i = 0;
FILE* numeri = fopen("numeri.txt", "r");
if (numeri == NULL) {
printf("Can't open file\n");
return 1;
}
while (count < 100 && fscanf(numeri, "%d", &num) == 1) {
a[count++] = num;
}
for (i = 0; i < count; i++) { printf("%d ", a[i]); }
return 0;
}
I am trying to read this input txt file with my C code:
4 3
1.4 4.6 1
1.6 6.65 1
7.8 1.45 0
7 -2 2
and separate them into rows and columns so that I can sort. I tried doing that but I kept getting weird numbers.
So I tried printing out the rows and columns after I read them from the file and the output was zero. I realized then that my code is not reading the numbers from my text file properly. I have tried different means to fix to no avail. Any help or pointers will be highly appreciated.
#include <stdio.h>
#include <string.h>
#include <stdbool.h> //for bool
int main(){
setvbuf(stdout, NULL,_IONBF, 0);
int c;
FILE *file;
FILE *infile;
char filename[99];
char choice;
int rows, columns;
//while(choice == 'y' || choice == 'Y'){
printf("%s", "Enter file name: ");
fgets(filename, 99, stdin);
char *p = strchr(filename, '\n'); // p will point to the newline in filename
if(p) *p = 0;
file = fopen(filename, "r");
if (file) {
while ((c = getc(file)) != EOF)
putchar(c);
fclose(file);
}
else{
puts("FILE NOT FOUND");
}
//read rows and columns from file
printf("%s","\n");
fscanf(file, "%d", &rows);
fscanf(file, "%d", &columns);
printf("%d", rows);
printf("%d", columns);
}
Problem 1
int rows = 0;
int columns = 0;
float matrix[rows][columns];
float sumOfRows[rows];
is not right.
After that, the number of elements in matrix and sumOfRows is fixed. They won't change if you change the values of rows and columns later in your program.
You need to read the values of rows and columns first before you define matrix and sumOfRows.
Problem 2
fscanf(file, "%d", &matrix[rows][columns]);
printf("%f",matrix[rows][columns]);
are not right either. Given the defition of matrix, use of matrix[rows][columns] is not right. They access the array using out of bounds indices.
Remember that given an array of size N, the valid indices are 0 to N-1.
Here's one way to proceed to resolve your problems:
fscanf(file, "%d", &rows); // Use %d, not %f
fscanf(file, "%d", &columns); // Use %d, not %f
// Now define the arrays.
float matrix[rows][columns];
float sumOfRows[rows];
// Read the data of matrix
for (int i = 0; i < rows; ++i )
{
for (int j = 0; j < columns; ++j )
{
fscanf(file, "%f", &matrix[i][j]); // Use %f, not %d
}
}
Your problem (actually, two problems) are in the if (file) {... block. First, you use a loop to read all characters from the file. Because of that, at the end of the loop you are also at the end of the file. Any further calls to fscanf result in undefined behavior.
Second, if the file did not open, you print a message (to the wrong output) and still continue to the fscanf part, which definitely leads to undefined behavior.
Solution: Remove the while loop and fix the error handling code:
if(file) {
// Nothing!
} else {
perror(filename);
return 1; // or return EXIT_FAILURE;
}
the first to say is that I'm totally new to coding, so plz forgive my mistakes.
I'm now trying to read from a txt file which is rather large, it has about 1000000 lines and 4 cols
56.154 59.365 98.3333 20.11125
98.54 69.3645 52.3333 69.876
76.154 29.365 34.3333 75.114
37.154 57.365 7.0 24.768
........
........
I want to read them all and store them into a matrix, here is my code:
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
int main()
{
int i;
int j;
/*matrix*/
int** mat=malloc(1000000*sizeof(int));
for(i=0;i<1000000;++i)
mat[i]=malloc(4*sizeof(int));
FILE *file;
file=fopen("12345.txt", "r");
for(i = 0; i < 1000; i++)
{
for(j = 0; j < 4; j++)
{
if (!fscanf(file, " %c", &mat[i][j]))
break;
mat[i][j] -= '0'; /* I found it from internet but it doesn't work*/
printf("\n",mat[i][j]);
}
}
fclose(file);
}
The result is that I got nothing in my matrix. I hope u can help. Thanks in advance for any help.
Many Issues, consider following, and of course see comments
int main()
{
int i;
int j;
/*matrix*/
/*Use double , you have floating numbers not int*/
double** mat=malloc(1000000*sizeof(double*));
for(i=0;i<1000000;++i)
mat[i]=malloc(4*sizeof(double));
FILE *file;
file=fopen("1234.txt", "r");
for(i = 0; i < 1000; i++)
{
for(j = 0; j < 4; j++)
{
//Use lf format specifier, %c is for character
if (!fscanf(file, "%lf", &mat[i][j]))
break;
// mat[i][j] -= '0';
printf("%lf\n",mat[i][j]); //Use lf format specifier, \n is for new line
}
}
fclose(file);
}
fscanf( "%c", ... ) only scans one single character (e.g. '5'). By subtracting '0' you get the integer value 5 from the character '5'. You can use "%d" to scan integers that consist only of digits (not including formatting characters), or "%f" for floats (not sure if 56.154 is to be read as "56 thousand 154" (continental europe) or "56 plus 154/1000" (GB / USA) (the rest of the world: don't be offended I just don't know)
printf( "\n", ... ): you forgot to use any formatting string such as %d (int), %f (float) ... So your parameter will not be printed, just the newline itself.
int** mat=malloc(1000000*sizeof(int)); You're allocating an array of int * here, so it should be int** mat=malloc(1000000*sizeof(int *));
Edit: I've looked again at your text file and have seen numbers like 98.54 that can't be formatted integers. So it's quite clear you will need float or double instead if int for your array and use "%f" for float or "%lf" for double in both fscanf() and printf()
You have a couple of things wrong with your code here.
First off you create a matrix of int yet you are reading in float values it looks like. You probably want to use double
Second, when you are reading a double you should use
fscanf(file, "%lf", &some_double); // fscanf(file, "%d", &some_int); for integers
Also when you are allocating your matrix, your first malloc you should pass
sizeof(double *) // or int * if you are really trying to use integers
Finally your line that does:
mat[i][j] -= '0'
What are you trying to accomplish here? You're taking the int that you (tried) to read in and subtracting off '0'...
Edit I also notice that you are hard coding the number of lines you are reading, I wouldn't do that unless you know the format of the file.
I just figured out how to do this with integers so decided to give it a go with strings and got stuck.
Here is what is in my file "kw":
keyword0
keyword1
keyword2
keyword3
With this current code I'm getting "error: format '%s' expects argument of type 'char *', but argument 3 has type 'char **'
#include <stdio.h>
int main () {
FILE *pFile;
pFile = fopen("kw", "r");
if (pFile != NULL) {
char *a[3];
int i;
for(i = 0; i <= 3; i++) {
fscanf(pFile, "%s", &a[i]);
printf("%s\n", a[i]);
}
}
return 0;
}
Could someone point me in the right direction here? Thank you.
There are several problems with this code:
You are going through four elements of the array a, while the array has only three elements.
You did not allocate space for the strings that you are reading with scanf.
You do not pass the address of address when you read strings.
To fix the first problem, change <= for != or <, like this:
for(i = 0; i != 3; i++)
To fix the second and the third problem, use malloc:
a[i] = malloc(21*sizeof(char));
fscanf(pFile, "%20s", a[i]);
Once you are done with the data that you allocated, don't forget to free the strings:
for(i = 0; i != 3; i++) {
free(a[i]);
}
I currently have code that reads 4 lines and I want to be able to change that until EOF or my MAX const int value. I can not get the !EOF to work right and was wondering how would I change my code to accomplish this?
Thanks in advance
#include <stdio.h>
struct record{
char name[2];
int arrival_time;
int job_length;
int job_priority;
};
const int MAX = 40;
int main(void)
{
struct record jobs[MAX];
int i = 0;
int j;
FILE *f = fopen("data.dat","rb");
while (fscanf(f, "%s %d %d %d", &jobs[i].name, &jobs[i].arrival_time,
&jobs[i].job_length, &jobs[i].job_priority) == 4 && i < MAX)
i++;
for (j = 0; j < i; j++)
printf("%s %d %d %d\n", jobs[j].name, jobs[j].arrival_time,
jobs[j].job_length, jobs[j].job_priority);
fclose(f);
return(0);
}
Something like
while (fscanf(f, " %s ", &etc) != EOF) {
}
Then use feof(f) to check if it was a fscanf error or actually EOF.
Your code seems to do what you want, except:
char name[2];
Names will probably be longer than 1 character.
FILE *f = fopen("data.dat","rb");
You seem to be reading text ("r") file, not binary ("rb").
&jobs[i].name should be jobs[i].name
You need to change the order of the tests in your while() loop - you must test i < MAX before calling fscanf(), or else you'll potentially call it one too many times (you should also be passing jobs[i].name without the & to fscanf):
while (i < MAX && fscanf(f, "%s %d %d %d", jobs[i].name, &jobs[i].arrival_time,
&jobs[i].job_length, &jobs[i].job_priority) == 4)
Personnaly, I would code like this:
for(i=0 ; i<MAX ; ++i) {
fscanf(f, "%s %d %d %d", &jobs[i].name, &jobs[i].arrival_time,
&jobs[i].job_length, &jobs[i].job_priority);
if(ferror(f) || feof(f)) break;
}
The key point is that, at the best of my knowledge, you cannot know that a file is come to end without trying to read it. That is the reason why I check feof() and ferror() after having read data.
At the end of the loop, the variable i contains the number of read data