While doing some practice for an upcoming assignment I ran into a problem using fscanf and trying to throw a notice when the incorrect format is entered into the program. I'm pretty sure I have to use the return of fscanf, but can't figure out how to use it inside my while loop. Currently the program loops continuously when a value such as "a3" is entered, yet "3e" works almost fine, except it outputs the number 3 twice.
Working scanf code:
int intGet( int min, int max ) {
int input = 0;
char temp = ' ';
printf("Enter a number in between [%d-%d]: ", min, max);
if (scanf("%d%c", &input, &temp) != 2){
errorNo = 1;
return EXIT_FAILURE;
}
if (temp != '\n'){
errorNo = 2;
return EXIT_FAILURE;
}
if (input < min || input > max){
errorNo = 3;
return EXIT_FAILURE;
}
else {
printf("Read %d\n", input);
}
return EXIT_SUCCESS;
fscanf code along the same idea, which loops continuously:
int intGet( int min, int max ) {
int counterValid = 0;
int counterInvalid = 0;
int entry = 0;
int total = 0;
int input = 0;
int check = 0;
char temp = ' ';
FILE *fp;
fp = fopen("02_num.txt", "r");
if (!fp)
{
perror("fopen()");
exit(EXIT_FAILURE);
}
printf("----------------------------------------------------------\n");
printf("Entry\tInvalid\tValid\tNumber\n");
printf("----------------------------------------------------------\n");
fscanf(fp, "%*[^\n]\n"); //skips first line (min and max)
while (check != EOF){
check = fscanf(fp, "%d%c", &input, &temp);
if (check == EOF){
exit(EXIT_SUCCESS);
}
if (check != 2){
counterInvalid += 1;
entry += 1;
printf("%d\t*\t\t%d\tIncorrect Format\n", entry, input);
}
if (temp != '\n'){
counterInvalid += 1;
entry += 1;
printf("%d\t*\t\t%d\tExtra Characters\n", entry, input);
}
if (input < min || input > max){
counterInvalid += 1;
entry += 1;
printf("%d\t*\t\t%d\tInput Number out of Range\n", entry, input);
}
else{
counterValid += 1;
entry +=1;
total += input;
printf("%d\t\t*\t%d\n", entry, input);
}
}
printf("----------------------------------------------------------\n");
entry +=1;
printf("%d\t%d\t%d\t%d\n", entry, counterInvalid, counterValid, total);
return EXIT_SUCCESS;
}
This code will then output a table that looks something like this:
*****************************************************
Entry Invalid Valid Number
1 * 32
*****************************************************
// adds invalid and valid entry totals, displays then here, adds totals of valid numbers and also outputs them here.
02_num.txt file that was being used in this code, first two numbers are the min and max, read in another function.
1 15 //min and max
23
45
67
8990
3e
12
a3
Things I have tried to work with the if/while loop:
Defining a variable to record the return value of fscanf (currently the closest):
while (check != EOF){
check = fscanf(fp, "%d%c", &input, &temp);
if (check != 2){
counterInvalid += 1;
entry += 1;
printf("%d\t*\t\t%d\tIncorrect Format\n", entry, input);
}
Checking the return value in the if statement as well (scans the file twice and doesn't output properly):
while (fscanf(fp, "%d", &input) != EOF){
if (fscanf(fp, "%d%c", &input, &temp) != 2){
counterInvalid += 1;
entry += 1;
printf("%d\t*\t\t%d\tIncorrect Format\n", entry, input);
}
If there is any information I am missing please let me know, i'm just a bit stuck here.. have been for the past couple days. Probably just a stupid mistake i'm missing but thanks in advance!
The problem with the loop is what you do when fscanf returns zero. Among other things, it means that if you call fscanf again with the same format string, the result is going to be zero, because the problem in the input that lead to you getting zero in the first place has not been addressed.
You need to add code for skipping the line when you get zero back from fscanf - for example, your fscanf(fp, "%*[^\n]"); fscanf(fp, "%*1[\n]");, as modified by Jonathan Leffler and chux, will work.
Related
I've this difficult assignment where I only have to use for loop.. so we're not allowed to use while or do.. while loop also else statement.. am trying to take the user input until he/she input EOF, so that the program will return the average number. So I wrote the code and ran it but whenever I enter ctrl+z (EOF) the program wont stop or even return the average values :(
for (int i = 0; i < 50; i++) {
printf("Please enter employee rank: ");
scanf("%d", &newnum);
sumavg += newnum;
counter++;
avg = sumavg / counter;
if (newnum < 8) {
summ += newnum;
ccoun++;
avgle = summ / ccoun;
}
}
printf("the avg : %d", avg);
printf("\nthe avg : %d \n", avgle);
So, I updated the code and there is a minor problem here.. idk why the program don't respond from the first time I enter EOF..
for (int i = 0; i < BN; i++) {
printf("Please enter employee rank: ");
result = scanf("%d", &newnum);
if (result == EOF)
break;
sumavg += newnum;
counter++;
avg = sumavg / counter;
if (newnum < 8) {
summ += newnum;
ccoun++;
avgle = summ / ccoun;
}
You can just check the return value of scanf(). From the scanf() manual,
The value EOF is returned if the end of input is reached before
either the first successful conversion or a matching failure
occurs. EOF is also returned if a read error occurs, in which
case the error indicator for the stream (see ferror(3)) is set,
and errno is set to indicate the error.
#include <stdio.h>
int main(void)
{
int newNum[50];
for (int i = 0; i < 50; i++)
{
int ret = scanf("%d", &newNum[i]);
if (ret != 1) /* 1 int to read */
{
if (ret == EOF)
{
/* input error might also have occured here, check errno to be sure */
break;
}
}
/* code */
}
return 0;
}
or directly in the for loop,
for (int i = 0; i < ARRAY_SIZE && scanf("%d", &newNum[i]) == 1; i++)
{
/* code */
}
scanf("%d", &foo) doesn't store EOF in foo on end of file. But you are allready checking for EOF when doing scanf, use that to break your loop.
for(....)
{
if(scanf(...) != EOF)
{
....
}
else
{
break;
}
}
The code above has only a minor problem, it does detect IO errors and end of file, but not parse errors. It would be better to write something like this:
for(int i=0; ...)
{
int n;
int err;
err = scanf("%d", &n);
if ( err == 1)
{
/* Process input */
newnum[i] = n;
}
else if (err == EOF && ferror(stdin))
{
/* IO error */
perror ("Failure to read from standard input");
exit(EXIT_FAILURE);
}
else if (err == EOF)
break;
else
{
/* Handle parse errors */
}
}
Naturally you have to fit error handling to your needs.
When I need EOF from stdin I run program as bellow.
./a.out <<DATA
1
2
3
4
5
6
7
8
9
10
DATA
This works fine on Linux. Not sure how is works on other platform
writing a program that will be finding min, max, avg of values entered by user. Having trouble writing something that will check to make sure there are only postive integers entered and produce an error message. heres my for statement that is reading the input so far:
for (int value = 0; value <= numofvals; ++value) {
printf("Value %d: %f\n", value, val_input);
scanf("%f", &val_input);
}
mind you I've been learning code for about 3 weeks and was just introduced to loops this week so my understanding is rudimentary at best!
First, don't use scanf. If stdin doesn't match what it expects it will leave it in the buffer and just keep rereading the same wrong input. It's very frustrating to debug.
const int max_values = 10;
for (int i = 0; i <= max_values; i++) {
int value;
if( scanf("%d", &value) == 1 ) {
printf("Got %d\n", value);
}
else {
fprintf(stderr, "I don't recognize that as a number.\n");
}
}
Watch what happens when you feed it something that isn't a number. It just keeps trying to read the bad line over and over again.
$ ./test
1
Got 1
2
Got 2
3
Got 3
foo
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
Instead, use fgets to reliably read the whole line and sscanf to parse it. %f is for floats, decimal numbers. Use %d to recognize only integers. Then check if it's positive.
#include <stdio.h>
int main() {
const size_t max_values = 10;
int values[max_values];
char buf[1024];
size_t i = 0;
while(
// Keep reading until we have enough values.
(i < max_values) &&
// Read the line, but stop if there's no more input.
(fgets(buf, sizeof(buf), stdin) != NULL)
) {
int value;
// Parse the line as an integer.
// If it doesn't parse, tell the user and skip to the next line.
if( sscanf(buf, "%d", &value) != 1 ) {
fprintf(stderr, "I don't recognize that as a number.\n");
continue;
}
// Check if it's a positive integer.
// If it isn't, tell the user and skip to the next line.
if( value < 0 ) {
fprintf(stderr, "Only positive integers, please.\n");
continue;
}
// We got this far, it must be a positive integer!
// Assign it and increment our position in the array.
values[i] = value;
i++;
}
// Print the array.
for( i = 0; i < max_values; i++ ) {
printf("%d\n", values[i]);
}
}
Note that because the user might input bad values we can't use a simple for loop. Instead we loop until either we've read enough valid values, or there's no more input.
Something easy like this may work for you:
int n;
int ret;
for (;;) {
ret = scanf("%d", &n);
if (ret == EOF)
break;
if (ret != 1) {
puts("Not an integer");
for (;;)
if (getchar() == '\n')
break;
continue;
}
if (n < 0) {
puts("Not a positive integer");
continue;
}
printf("Correct value %d\n", n);
/* Do your min/max/avg calculation */
}
/* Print your results here */
This is just an example and assumes you do not need to read floating point numbers and then check if they are integers, as well as a few other things. But for starters, it is simple and you can work on top of it.
To break out of the loop, you need to pass EOF (typically Ctrl+D in Linux/macOS terminals, Ctrl+Z in Windows ones).
An easy and portable solution
#include <limits.h>
#include <stdio.h>
int get_positive_number() {
char buff[1024];
int value, ch;
while (1) {
printf("Enter positive number: ");
if (fgets(buff, 1023, stdin) == NULL) {
printf("Incorrect Input\n");
// Portable way to empty input buffer
while ((ch = getchar()) != '\n' && ch != EOF)
;
continue;
}
if (sscanf(buff, "%d", &value) != 1 || value < 0) {
printf("Please enter a valid input\n");
} else {
break;
}
}
return value;
}
void solution() {
// Handling malformed input
// Memory Efficient (without using array to store values)
int n;
int min = INT_MAX;
int max = INT_MIN;
double avg = 0;
printf("Enter number of elements: ");
scanf("%d", &n);
getc(stdin);
int value;
for (int i = 0; i < n; i++) {
value = get_positive_number();
if (value > 0) {
if (min > value) {
min = value;
}
if (max < value) {
max = value;
}
avg += value;
}
}
avg = avg / n;
printf("Min = %d\nMax = %d\nAverage = %lf\n", min, max, avg);
}
int main() {
solution();
return 0;
}
Output:
Enter number of elements: 3
Enter positive number: 1
Enter positive number: 2
Enter positive number: a
Please enter a valid input
Enter positive number: -1
Please enter a valid input
Enter positive number: 1
Min = 1
Max = 2
Average = 1.333333
I've looked around and haven't seen this question answered yet. Basically I am trying to create an array of integers from text files that have sequences of integers e.g, 2 5 2 9 1 0 3 53 7 . I want to print an error message if line in the text file exceed 10 integers. There is only one line in the text file.
Here is my code so far:
#include <stdio.h>
#include <stdlib.h>
int main()
{
FILE *file = fopen("somenumbers.txt", "r");
int integers[10];
int i=0;
int num;
if (file == NULL)
{
printf("Error Reading File\n");
exit (0);
}
while(fscanf(file, "%d", &num) > 0) {
integers[i] = num;
i++;
}
for (i = 0; i < 16; i++)
{
printf("Number is: %d\n\n", integers[i]);
}
fclose(file);
return 0;
}
Should I check the check the contents of the array after it is finished being created or during the initial iteration through the line? Are there any functions that would make it easy to determine if the line in the text file is larger than the limit(10)?
You must check in while loop as below;
while(fscanf(file, "%d", &num) > 0) {
if (i >= 10) {
printf("error\n");
break;
}
integers[i++] = num;
}
You should ensure that you never access integers[10], otherwise it's array out-of-bounds error which results in undefined behavior (i.e. literally anything can happen after that). So if you succeeded in reading 11-th number (which should go into integers[10]), you should stop the loop immediately.
The reason you are getting the error is the size of integers array being 10. Due to that size, if you read more than 10 integers, you will have a segment violation problem.
To find out that you have more than 10 integers, all you need to understand you should give an error is to read the 11th integer. So instead of declaring the array with size 10, switch it to 11. Then, when you read the 11th integer you may print an error message and exit properly.
Also, you may want to bound the loop printing the numbers by the amount of integers you have read.
Below is a sample code, based on yours, that implements the fixes I mentioned.
#include <stdio.h>
#include <stdlib.h>
int main()
{
FILE *file = fopen("somenumbers.txt", "r");
int integers[11];
int i=0, k=0;
int num;
if (file == NULL)
{
printf("Error Reading File\n");
exit (0);
}
while(fscanf(file, "%d", &num) > 0) {
integers[i] = num;
if(k++ == 10) {
{
printf("Too many integers!!!\n"); /* or any other error message you'd like */
exit (0);
}
}
/* loop iterates until k integers are printed. k contains the # of integers read. */
for (i = 0; i < k; i++)
{
printf("Number is: %d\n\n", integers[i]);
}
fclose(file);
return 0;
}
Check before:
...
while (fscanf(file, "%d", &num) > 0) {
if (i >= 10) {
/* handle error */
break; /* or return */
}
...
to prevent trying to access an array element that does not exist
You have two errors:
1) When reading, you may write the input value outside the array boundary
2) When printing, you for sure acces outside array boundary.
Try this instead:
while(fscanf(file, "%d", &num) > 0) {
integers[i] = num;
i++;
if (i == 10)
{
break; // Can't store more value so stop the loop using break
}
}
// Save the number of values read
int total = i;
for (i = 0; i < total; i++)
// ^^^^ notice
{
printf("Number is: %d\n\n", integers[i]);
}
As an alternative to break you can put the check of i into the while condition like:
while(i < 10 && fscanf(file, "%d", &num) > 0) {
//^^^^^^ notice
integers[i] = num;
i++;
}
You have some issues with your code:
The code posted is prone to buffer overflow, as you are not checking if more than 10 integers have been found. This means you will be accessing outside the bounds of integers[10], which only causes undefined behavour.
Since you want to read one integer at a time with fscanf(), you should use:
while (fscanf(file, "%d", &num) == 1)
Instead of:
while(fscanf(file, "%d", &num) > 0)
fscanf() returns the number of values read, and using 1 instead of > 0 would make more sense in this case.
This segment here:
for (i = 0; i < 16; i++)
{
printf("Number is: %d\n\n", integers[i]);
}
is accessing beyond bounds of integers[10]. You need to change the guard so you don't exceed the limit of 10 integers.
Your code can look like this:
#include <stdio.h>
#include <stdlib.h>
#define MAXINT 10
int main(void) {
FILE *file;
int integers[MAXINT], num;
size_t count = 0;
file = fopen("somenumbers.txt", "r");
if (!file) {
fprintf(stderr, "%s\n", "Error reading file");
exit(EXIT_FAILURE);
}
while (fscanf(file, "%d", &num) == 1) {
if (count == MAXINT) {
printf("More than %d integers found!\n", MAXINT);
exit(EXIT_FAILURE);
}
integers[count++] = num;
}
printf("Success! No more than %d integers found:\n", MAXINT);
for (size_t i = 0; i < count; i++) {
printf("integers[%zu] = %d\n", i, integers[i]);
}
fclose(file);
return 0;
}
I'm trying to take the input of floating numbers from a file and arrange it into an array.
The only trouble is that I don't know exactly how many floating numbers there will be each time though I do know that the max amount of floating numbers is 1000.
What I need to do is have fscanf take all the floating numbers but then stop at the next line, which is full of integers.
Here is what I have so far for this section:
for (repetition = 0; repetition <= 1000; repetition++)
{
fscanf(userFile, "%f", &itemPrice[itemNumber]);
itemNumber++;
}
But unfortunately, this continues on to assign array values to all of the other values in the next several lines.
I found another user input, auctionItems and used that to control the array length using while(itemNumber < auctionItems)
The return value of fscanf is the number of items successfully read. Use that to decide when to stop.
#include <stdio.h>
int main(int argc,char * argv[])
{
int i;
float ff[1000];
char next_text[17];
for (i=0; i < 1000; i++) {
int n_read;
n_read = fscanf(stdin, " %f", &( ff[i] ));
if (n_read < 1) {
fscanf(stdin, "%16s", next_text);
next_text[16] = (char) 0;
printf("Next text: '%s'\n", next_text);
break;
}
}
printf("Read %d items, %f .. %f\n",i,ff[0],ff[i-1]);
return 0;
}
Maybe you could try this method using fgetc and fputc:
for (repetition = 0; itemPrice <= 1000; repetition++)
{
int c = fgetc(userFile);
if (c == '\n' || c == EOF) break;
fputc(c);
fscanf(userFile, "%f", &itemPrice[itemNumber]);
itemNumber++;
}
char input[MAX];
while(fgets(input, MAX, userFile) != NULL){
sscanf(input, "%lf", &itemPrice[itemNumber++]);
}
OP is fairly close. Just stop when scanning fails.
fscanf() returns the number of fields scanned or EOF. In this case, checking for 1 is sufficient.
// for (repetition = 0; itemPrice <= 1000; repetition++) Use <, not <= #Arpit
for (i = 0; i < 1000; )
{
int retval = fscanf(userFile, "%f", &itemPrice[i]);
if (retval != 1) break;
i++;
}
A robust solution would detect unexpected data. This solution simple goes until the end-of-file or non-float text is encountered.
[Edit]
It appears OP has only 1 line of floats. In that case code could read the whole line and then parse the buffer.
#define CHAR_PER_FLOAT_MAX 20
char buf[1000*(CHAR_PER_FLOAT_MAX + 1)]; // Some large buffer
if (fgets(buf, sizeof buf, input)== NULL) return; // EOF or IO error
char *p = buf;
for (i = 0; i < 1000; ) {
int n = 0;
if (sscanf(p, "%f %n", &itemPrice[i], &n) != 1) break;
p += n;
i++;
}
if (*p) Handle_ExtraTextOnLine();
foo(itemPrice, i); // Use data
Another approach is to read direct from the file 1 float at a time and then look at the following white-space for an end-of-line. Less elegant.
for (i = 0; i < 1000; ) {
if (fscanf(input, "%f", &itemPrice[i]) != 1) {
// need to add code to consume the rest of the line if processing is to continue.
break;
}
i++;
// look for standard white-space
char buf[2];
while (fscanf(input, "%1[ \f\n\r\t\v]", buf) == 1) {
if (buf[0] == '\n') break;
}
}
foo(itemPrice, i); // Use data
I've been having some problems with this code below...
The main idea of the code is to read line by line and convert chars strings into floats and save the floats in a array called nfloat.
The input is a .txt containing this: n = the number of strings, in this case n = 3
3
[9.3,1.2,87.9]
[1.0,1.0]
[0.0,0.0,1.0]
The first number, 3 is the number of vectors as we can see in the image, but that number isn't static, the input can be 5 or 7, etc instead of 3.
So far, I've started doing the following, (for only 1 vector case) but the code has some memory errors I think:
int main(){
int n; //number of string, comes in the input
scanf("%d\n", &n);
char *line = NULL;
size_t len = 0;
ssize_t read;
read = getline(&line,&len,stdin); //here the program assigns memory for the 1st string
int numsvector = NumsVector(line, read);//calculate the amount of numbers in the strng
float nfloat[numsvector];
int i;
for (i = 0; i < numsvector; ++i)
{
if(numsvector == 1){
sscanf(line, "[%f]", &nfloat[i]);
}
else if(numsvector == 2){
if(i == 0) {
sscanf(line, "[%f,", &nfloat[i]);
printf("%f ", nfloat[i]);
}
else if(i == (numsvector-1)){
sscanf((line+1), "%f]", &nfloat[i]);
printf("%f\n", nfloat[i]);
}
}
else { //Here is where I think the problems are
if(i == 0) {
sscanf(line, "[%f,", &nfloat[i]);
printf("%f\n", nfloat[i]);
}
else if(i == (numsvector-1)) {
sscanf((line+1+(4*i)), "%f]", &nfloat[i]);
printf("%f\n", nfloat[i]);
}
else {
sscanf((line+1+(4*i)), "%f,", &nfloat[i]);
printf("%f\n", nfloat[i]);
}
}
}
Well, the problems come with the sscanf instructions I think, in the case of a string with two floats or one, the code works fine but in the case of 3 or more floats, the code doesn't work well and I can't understand why...
Here I attach the function too, but It seems to be correct... the focus of the problem remains on the main.
int NumsVector(char *linea, ssize_t size){
int numsvector = 1; //minimum value = 1
int n;
for(n = 2; n<= size; n++){
if (linea[n] != '[' && linea[n] != ']'){
if(linea[n] == 44){
numsvector = numsvector + 1;
}
}
}
return numsvector;
}
Please could someone help me understand where is the problem?
Ok - if you replace your current for loop with this, your nfloat array should end up with the right numbers in it.
/* Replaces the end ] with a , */
line[strlen(line) - 1] = ',';
/* creates a new pointer, pointing after the first [ in the original string */
char *p = line + 1;
do
{
/* grabs up to the next comma as a float */
sscanf(p, "%f,", &nfloat[i]);
/* prints the float it's just grabbed to 2 dp */
printf("%.2f\n",nfloat[i]);
/* moves pointer forward to next comma */
while (*(p++) != ',');
}
while (++i < numsvector); /* stops when you've got the expected number */