I have a problem with sscanf function. To be more specific I want read a float from a txt file (I want only one float for line) but sscanf doesn't recognize these situations:
3.4t
or
4.t6
or
4.5 6.5
or
(this is an empty line)
I use this code:
#define LUNRIGA 200
char riga[LUNRIGA+1];
while (fgets(riga,LUNRIGA,f) != NULL) {
r = sscanf(riga,"%f",&numeri[i]);
if (r == 1) { /* riga valida */
printf("OK");
}else{
printf("Error");
return 1;
}
}
sscanf is notoriously picky about the input. You will have better luck using strtod or strtol - they can read a value even if it's followed by junk. Change your code as follows:
#define LUNRIGA 200
char riga[LUNRIGA+1];
char* tempPtr;
while (fgets(riga,LUNRIGA,f) != NULL) {
numeri[i] = strtof( riga, &tempPtr );
if (tempPtr > riga) { /* riga valida */
printf("OK");
}
else {
printf("Error");
return 1;
}
}
Note by the way that you don't seem to increment i in your loop - you might want to see if that's actually what you want, or if you would like to increment it every time you get a valid number (assuming you don't just want the last value, but all of them...)
As a little demo of the behavior of strtod, I wrote a few lines of code:
#include <stdio.h>
#include <stdlib.h>
int main(void) {
char* s1="123.45t";
char* p1;
char* s2 = " notanumber";
double d1, d2;
d1 = strtod(s1, &p1);
printf("the number is %.2lf; the pointer is now %p; string is at %p\n", d1, s1, p1);
d2 = strtod(s2, &p1);
printf("the number is %.2lf; the pointer is now %p; string is at %p\n", d2, s2, p1);
}
The output of this is:
The number is 123.45; the pointer is now 0x400668; string is at 0x40066e
The number is 0.00; the pointer is now 0x400670; string is at 0x400670
As you can see, when reading garbage the pointer returned points to the start of the string - indicating "failed". When it is successful, the pointer is pointing to "where I stopped reading", which is "after successfully converting a bit of string to double.
If you want to be sure there's no junk on the line, you can use the %n directive to find out where conversion stops and decide what to do about what comes afterwards on the line:
char riga[LUNRIGA];
float numeri[NUM_VALUES];
int offset;
int i;
for (i = 0; i < NUM_VALUES && fgets(riga, sizeof(riga), f) != NULL; i++)
{
int r = sscanf(riga, "%f%n", &numeri[i], &offset);
if (r == 1 && riga[offset] == '\n')
printf("OK (got %f from <<%s>>\n", numeri[i], riga);
else
{
printf("Error processing <<%s>>\n", riga);
return 1;
}
}
You can do some extra processing before the sscanf(), for example to check that you read a newline (so there isn't the residue of an extra long line still to be read) and to remove the newline (but then you need to change the condition).
Note the use of sizeof(riga), and the check for not overflowing numeri by imposing a for loop on the code, and the presence of a newline at the end of each message printed.
Related
I have this code and I need help converting the comments to c code
// if the input of scanf() is "q"
{
break;
}
else
{
// convert to int
}
Firstly, how do I check if an input is a certain character. Secondly, how do I turn a string into an integer. Example: "123" -> 123
Things I've tried, that didn't work: (it is possible that I implemented these solutions incorrectly)
how does scanf() check if the input is an integer or character?
Convert char to int in C and C++
I am not using any standard libraries except for stdio.h to print some logging information on the window
you have to know also that any string is terminated by null character which is '\0' to indicate the termination of the string , also you have to check is the user entered characters not numbers and so on (that's not implemented in this code).
I also handled if negative numbers are entered.
but you have to handle if the user entered decimals numbers , to sum up . there are so many cases to handle.
and here the edited code :
#include <stdio.h>
int main(){
char inputString[100];
printf("enter the input:\n");
scanf("%s", &inputString);
if(inputString[0] == 'q' && inputString[1] == '\0' )
{
printf("quiting\n");
//break;
}
else {
int i = 0;
int isNegative = 0;
int number = 0;
// check if the number is negative
if (inputString[0] == '-') {
isNegative = 1;
i = 1;
}
// convert to int
for ( ;inputString[i] != '\0' ; i++) {
number *= 10;
number += (inputString[i] - '0');
}
if(isNegative == 1)
number *= -1;
printf("you entered %d\n", number);
}
return 0;
}
The fundamental question here is, Do you want to use scanf?
scanf is everyone's favorite library function for easily reading in values. scanf has an input specifier, %d, for reading in integers.
And it has a different input specifier, %s, for reading in arbitrary strings.
But scanf does not have any single input specifier that means, "Read in an integer as an integer if the user types a valid integer, but if the user types something like "q", have a way so I can get my hands on that string instead."
Unless you want to move mountains and implement your own general-purpose input library from scratch, I think you have basically three options:
Use scanf with %d to read integers as integers, but check scanf's return value, and if scanf fails to read an integer, use that failure to terminate input.
Use scanf with %s to read the user's input as a string, so you can then explicitly test if it's a "q" or not. If not, convert it to an integer by hand. (More on this below.)
Don't use scanf at all. Use fgets to read the user's input as a whole line of text. Then see if it's a "q" or not. If not, convert it to an integer by hand.
Number 1 looks something like this:
while(some loop condition) {
printf("enter next integer, or 'q' to quit:\n");
if(scanf("%d", &i) != 1) {
/* end of input detected */
break;
}
do something with i value just read;
}
The only problem with this solution is that it won't just stop if the user types "q", as your original problem statement stipulated. It will also stop if the user types "x", or "hello", or control-D, or anything else that's not a valid integer. But that's also a good thing, in that your loop won't get confused if the user types something unexpected, that's neither "q" nor a valid integer.
My point is that explicitly checking scanf's return value like this is an excellent idea, in any program that uses scanf. You should always check to see that scanf succeeded, and do something different if it fails.
Number 2 would look something like this:
char tmpstr[20];
while(some loop condition) {
printf("enter next integer, or 'q' to quit:\n");
if(scanf("%19s", tmpstr) != 1) {
printf("input error\n");
exit(1);
}
if(strcmp(tmpstr, "q") == 0) {
/* end of input detected */
break;
}
i = atoi(tmpstr); /* convert string to integer */
do something with i value just read;
}
This will work well enough, although since it uses atoi it will have certain problems if the user types something other than "q" or a valid integer. (More on this below.)
Number 3 might look like this:
char tmpstr[20];
while(some loop condition) {
printf("enter next integer, or 'q' to quit:\n");
if(fgets(tmpstr, 20, stdin) == NULL) {
printf("input error\n");
exit(1);
}
if(strcmp(tmpstr, "q\n") == 0) {
/* end of input detected */
break;
}
i = atoi(tmpstr); /* convert string to integer */
do something with i value just read;
}
One thing to note here is that fgets includes the newline that the user typed in the string it returns, so if the user types "q" followed by the Enter key, you'll get a string back of "q\n", not just "q". You can take care of that either by explicitly looking for the string "q\n", which is kind of lame (although it's what I've done here), or by stripping the newline back off.
Finally, for both #2 and #3, there's the question of, what's the right way to convert the user's string to an integer, and what if it wasn't a valid integer? The easiest way to make the conversion is to call atoi, as my examples so far have shown, but it has the problem that its behavior on invalid input is undefined. In practice, it will usually (a) ignore trailing nonnumeric input and (b) if there's no numeric input at all, return 0. (That is, it will read "123x" as 123, and "xyz" as 0.) But this behavior is not guaranteed, so these days, most experts recommend not using atoi.
The recommended alternative is strtol, which looks like this:
char *endp;
i = strtol(tmpstr, &endp, 10); /* convert string to integer */
Unlike atoi, strtol has guaranteed behavior on invalid input. Among other things, after it returns, it leaves your auxiliary pointer endp pointing at the first character in the string it didn't use, which is one way you can determine whether the input was fully valid or not. Unfortunately, properly dealing with all of the ways the input might be invalid (including trailing garbage, leading garbage, and numbers too big to convert) is a surprisingly complicated challenge, which I am not going to belabor this answer with.
Here are some guidelines:
scanf("%s", &var) is incorrect: you should pass the maximum number of characters to store into the array var and pass the array without the & as it will automatically convert to a pointer to its first element when passed as an argument:
char var[100];
if (scanf("%99s", var) != 1) {
printf("premature end of file\n");
return 1;
}
to compare the string read to "q", you can use strcmp() declared in <string.h>:
if (strcmp(var, "q") == 0) {
printf("quitting\n");
return 0;
}
to convert the string to the number it represents, use strtol() declared in <stdlib.h>:
char *p;
long value = strtol(var, &p, 0);
testing for a proper conversion is tricky: strtol() updated p to point to the character after the number and set errno in case of range error:
errno = 0;
char *p;
long value = strtol(var, &p, 0);
if (p == var) {
printf("not a number: %s\n", p);
return 1;
}
if (*p != '\0') {
printf("extra characters: %s\n", p);
return 1;
}
if (errno) {
printf("conversion error: %s\n", strerror(errno));
return 1;
}
printf("the number entered is: %ld\n", value);
return 0;
Here is a complete program:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
char var[100];
char *p;
long value;
printf("Enter a number: ");
if (scanf("%99s", var) != 1) {
printf("premature end of file\n");
return 1;
}
if (strcmp(var, "q") == 0) {
printf("quitting\n");
return 0;
}
errno = 0;
value = strtol(var, &p, 0);
if (p == var) {
printf("not a number: %s\n", p);
return 1;
}
if (*p != '\0') {
printf("extra characters: %s\n", p);
return 1;
}
if (errno) {
printf("conversion error: %s\n", strerror(errno));
return 1;
}
printf("the number entered is: %ld\n", value);
return 0;
}
You can try this: (Assuming only positive integers needs to convert)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
// Write C code here
char var[100];
int numb_flag=1, i=0,number=0;
scanf("%s",var);
while(var[i]!='\0') { // Checking if the input is number
if(var[i]>=48 && var[i]<=57)
i++;
else {
numb_flag = 0;
break;
}
}
if(numb_flag==1) {
number = atoi(var);
printf("\nNumber: %d",number);
} else {
printf("\nNot A Number");
}
return 0;
}
//Mind that in order to be more precise you could also use atof().
//The function works the same way as atoi() but is able to convert float
// (returned value is 'double') the string s
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXILEN 100 /*change the value based on your needs*/
int main(){
int n, lim = MAXILEN;
char s[MAXILEN], *p = s, c;
/*taking the string from the input -- I do not use scanf*/
while(--lim > 0 && (c = getchar()) != EOF && c != '\n')
*p++ = c;
//here you can also do the check (if you want the '\n' char):
//if(c == '\n')
// *s++ = c;
*p = '\0';
if(s[0] == 'q' && s[1] == '\0')
exit(EXIT_SUCCESS); /*change the argument based on your needs*/
else
n = atoi(s);
printf("[DEBUG]: %d\n", n);
}
int main()
{
int f;
printf("Type your age");
scanf("%d", &f);
if(!isdigit(f))
{
printf("Digit");
}
else
{
printf("Is not a digit");
}
return 0;
}
No matter if a typed 6 or a always shows me the "Digit" message
isdigit() should be passed a char not an int. And your if-else logic is reversed:
int main() {
char f;
printf("Type your age");
scanf("%c", &f);
if (isdigit(f)) {
printf("Digit");
} else {
printf("Is not a digit");
}
return 0;
}
As mentioned in the comments, this will only work for a single digit age. Validating input is a major topic under the 'C' tag, a search will reveal many approaches to more robust validation.
%d is an integer specifier. Change int f to char f and parse as a character. You are always passing an int into isdigit, which is why it is always true.
There's actually no need to use isdigit at all here since scanf with the %d format specifier already guarantees that the characters will be digits with an optional leading sign. And there's a separate specifier to get rid of the leading sign, %u.
If what you input isn't of the correct format, scanf will tell you (since it returns the number of items successfully scanned).
So, for a simple solution, you can just use something like:
unsigned int age;
if (scanf("%u", &age) == 1) {
puts("Not a valid age");
return 1;
}
// Now it's a valid uint, though you may want to catch large values.
If you want robust code, you may have to put in a little more effort than a one-liner scanf("%d") - it's fine for one-time or throw-away programs but it has serious shortcomings for code intended to be used in real systems.
First, I would use the excellent string input routine in this answer(a) - it pretty much provides everything you need for prompted and checked user input.
Once you have the input as a string, strtoul allows you to do the same type of conversion as scanf but with the ability to also ensure there's no trailing rubbish on the line as well. This answer (from the same author) provides the means for doing that.
Tying that all together, you can use something like:
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
// Code to robustly get input from user.
#define OK 0 // Return codes - okay.
#define NO_INPUT 1 // - no input given.
#define TOO_LONG 2 // - input was too long.
static int getLine (
char *prmpt, // The prompt to use (NULL means no prompt).
char *buff, // The buffer to populate.
size_t sz // The size of the buffer.
) {
int ch, extra;
// Get line with buffer overrun protection.
if (prmpt != NULL) {
printf ("%s", prmpt);
fflush (stdout);
}
if (fgets (buff, sz, stdin) == NULL)
return NO_INPUT;
// If it was too long, there'll be no newline. In that case, we flush
// to end of line so that excess doesn't affect the next call.
if (buff[strlen(buff)-1] != '\n') {
extra = 0;
while (((ch = getchar()) != '\n') && (ch != EOF))
extra = 1;
return (extra == 1) ? TOO_LONG : OK;
}
// Otherwise remove newline and give string back to caller.
buff[strlen(buff)-1] = '\0';
return OK;
}
// Code to check string is valid unsigned integer and within range.
// Returns true if it passed all checks, false otherwise.
static int validateStrAsUInt(
char *str, // String to evaluate.
unsigned int minVal, // Minimum allowed value.
unsigned int maxVal, // Maximum allowed value.
unsigned int *pResult // Address of item to take value.
) {
char *nextChar;
unsigned long retVal = strtoul (str, &nextChar, 10);
// Ensure we used the *whole* string and that it wasn't empty.
if ((nextChar == str) || (*nextChar != '\0'))
return 0;
// Ensure it's within range.
if ((retVal < minVal) || (retVal > maxVal))
return 0;
// It's okay, send it back to caller.
*pResult = retVal;
return 1;
}
// Code for testing above functions.
int main(void) {
int retCode;
unsigned int age;
char buff[20];
// Get it as string, detecting input errors.
retCode = getLine ("Enter your age> ", buff, sizeof(buff));
if (retCode == NO_INPUT) {
printf ("\nError, no input given.\n");
return 1;
}
if (retCode == TOO_LONG) {
printf ("Error, input too long [%s]\n", buff);
return 1;
}
// Check string is valid age.
if (! validateStrAsUInt(buff, 0, 150, &age)) {
printf("Not a valid age (0-150)\n");
return 1;
}
// It's okay, print and exit.
printf("Age is valid: %u\n", age);
return 0;
}
(a) I'm reliably informed the author is actually quite clever, and very good looking :-)
I made this code:
/*here is the main function*/
int x , y=0, returned_value;
int *p = &x;
while (y<5){
printf("Please Insert X value\n");
returned_value = scanf ("%d" , p);
validate_input(returned_value, p);
y++;
}
the function:
void validate_input(int returned_value, int *p){
getchar();
while (returned_value!=1){
printf("invalid input, Insert Integers Only\n");
getchar();
returned_value = scanf("%d", p);
}
}
Although it is generally working very well but when I insert for example "1f1" , it accepts the "1" and does not report any error and when insert "f1f1f" it reads it twice and ruins the second read/scan and so on (i.e. first read print out "invalid input, Insert Integers Only" and instead for waiting again to re-read first read from the user, it continues to the second read and prints out again "invalid input, Insert Integers Only" again...
It needs a final touch and I read many answers but could not find it.
If you don't want to accept 1f1 as valid input then scanf is the wrong function to use as scanf returns as soon as it finds a match.
Instead read the whole line and then check if it only contains digits. After that you can call scanf
Something like:
#include <stdio.h>
int validateLine(char* line)
{
int ret=0;
// Allow negative numbers
if (*line && *line == '-') line++;
// Check that remaining chars are digits
while (*line && *line != '\n')
{
if (!isdigit(*line)) return 0; // Illegal char found
ret = 1; // Remember that at least one legal digit was found
++line;
}
return ret;
}
int main(void) {
char line[256];
int i;
int x , y=0;
while (y<5)
{
printf("Please Insert X value\n");
if (fgets(line, sizeof(line), stdin)) // Read the whole line
{
if (validateLine(line)) // Check that the line is a valid number
{
// Now it should be safe to call scanf - it shouldn't fail
// but check the return value in any case
if (1 != sscanf(line, "%d", &x))
{
printf("should never happen");
exit(1);
}
// Legal number found - break out of the "while (y<5)" loop
break;
}
else
{
printf("Illegal input %s", line);
}
}
y++;
}
if (y<5)
printf("x=%d\n", x);
else
printf("no more retries\n");
return 0;
}
Input
1f1
f1f1
-3
Output
Please Insert X value
Illegal input 1f1
Please Insert X value
Illegal input f1f1
Please Insert X value
Illegal input
Please Insert X value
x=-3
Another approach - avoid scanf
You could let your function calculate the number and thereby bypass scanf completely. It could look like:
#include <stdio.h>
int line2Int(char* line, int* x)
{
int negative = 0;
int ret=0;
int temp = 0;
if (*line && *line == '-')
{
line++;
negative = 1;
}
else if (*line && *line == '+') // If a + is to be accepted
line++; // If a + is to be accepted
while (*line && *line != '\n')
{
if (!isdigit(*line)) return 0; // Illegal char found
ret = 1;
// Update the number
temp = 10 * temp;
temp = temp + (*line - '0');
++line;
}
if (ret)
{
if (negative) temp = -temp;
*x = temp;
}
return ret;
}
int main(void) {
char line[256];
int i;
int x , y=0;
while (y<5)
{
printf("Please Insert X value\n");
if (fgets(line, sizeof(line), stdin))
{
if (line2Int(line, &x)) break; // Legal number - break out
printf("Illegal input %s", line);
}
y++;
}
if (y<5)
printf("x=%d\n", x);
else
printf("no more retries\n");
return 0;
}
Generally speaking, it is my opinion that you are better to read everything from the input (within the range of your buffer size, of course), and then validate the input is indeed the correct format.
In your case, you are seeing errors using a string like f1f1f because you are not reading in the entire STDIN buffer. As such, when you go to call scanf(...) again, there is still data inside of STDIN, so that is read in first instead of prompting the user to enter some more input. To read all of STDIN, you should do something the following (part of code borrowed from Paxdiablo's answer here: https://stackoverflow.com/a/4023921/2694511):
#include <stdio.h>
#include <string.h>
#include <stdlib.h> // Used for strtol
#define OK 0
#define NO_INPUT 1
#define TOO_LONG 2
#define NaN 3 // Not a Number (NaN)
int strIsInt(const char *ptrStr){
// Check if the string starts with a positive or negative sign
if(*ptrStr == '+' || *ptrStr == '-'){
// First character is a sign. Advance pointer position
ptrStr++;
}
// Now make sure the string (or the character after a positive/negative sign) is not null
if(*ptrStr == NULL){
return NaN;
}
while(*ptrStr != NULL){
// Check if the current character is a digit
// isdigit() returns zero for non-digit characters
if(isdigit( *ptrStr ) == 0){
// Not a digit
return NaN;
} // else, we'll increment the pointer and check the next character
ptrStr++;
}
// If we have made it this far, then we know that every character inside of the string is indeed a digit
// As such, we can go ahead and return a success response here
// (A success response, in this case, is any value other than NaN)
return 0;
}
static int getLine (char *prmpt, char *buff, size_t sz) {
int ch, extra;
// Get line with buffer overrun protection.
if (prmpt != NULL) {
printf ("%s", prmpt);
fflush (stdout);
}
if (fgets (buff, sz, stdin) == NULL)
return NO_INPUT;
// If it was too long, there'll be no newline. In that case, we flush
// to end of line so that excess doesn't affect the next call.
// (Per Chux suggestions in the comments, the "buff[0]" condition
// has been added here.)
if (buff[0] && buff[strlen(buff)-1] != '\n') {
extra = 0;
while (((ch = getchar()) != '\n') && (ch != EOF))
extra = 1;
return (extra == 1) ? TOO_LONG : OK;
}
// Otherwise remove newline and give string back to caller.
buff[strlen(buff)-1] = '\0';
return OK;
}
void validate_input(int responseCode, char *prompt, char *buffer, size_t bufferSize){
while( responseCode != OK ||
strIsInt( buffer ) == NaN )
{
printf("Invalid input.\nPlease enter integers only!\n");
fflush(stdout); /* It might be unnecessary to flush here because we'll flush STDOUT in the
getLine function anyway, but it is good practice to flush STDOUT when printing
important information. */
responseCode = getLine(prompt, buffer, bufferSize); // Read entire STDIN
}
// Finally, we know that the input is an integer
}
int main(int argc, char **argv){
char *prompt = "Please Insert X value\n";
int iResponseCode;
char cInputBuffer[100];
int x, y=0;
int *p = &x;
while(y < 5){
iResponseCode = getLine(prompt, cInputBuffer, sizeof(cInputBuffer)); // Read entire STDIN buffer
validate_input(iResponseCode, prompt, cInputBuffer, sizeof(cInputBuffer));
// Once validate_input finishes running, we should have a proper integer in our input buffer!
// Now we'll just convert it from a string to an integer, and store it in the P variable, as you
// were doing in your question.
sscanf(cInputBuffer, "%d", p);
y++;
}
}
Just as a disclaimer/note: I have not written in C for a very long time now, so I do apologize in advance if there are any error in this example. I also did not have an opportunity to compile and test this code before posting because I am in a rush right now.
If you're reading an input stream that you know is a text stream, but that you are not sure only consists of integers, then read strings.
Also, once you've read a string and want to see if it is an integer, use the standard library conversion routine strtol(). By doing this, you both get a confirmation that it was an integer and you get it converted for you into a long.
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
bool convert_to_long(long *number, const char *string)
{
char *endptr;
*number = strtol(string, &endptr, 10);
/* endptr will point to the first position in the string that could
* not be converted. If this position holds the string terminator
* '\0' the conversion went well. An empty input string will also
* result in *endptr == '\0', so we have to check this too, and fail
* if this happens.
*/
if (string[0] != '\0' && *endptr == '\0')
return false; /* conversion succesful */
return true; /* problem in conversion */
}
int main(void)
{
char buffer[256];
const int max_tries = 5;
int tries = 0;
long number;
while (tries++ < max_tries) {
puts("Enter input:");
scanf("%s", buffer);
if (!convert_to_long(&number, buffer))
break; /* returns false on success */
printf("Invalid input. '%s' is not integer, %d tries left\n", buffer,
max_tries - tries);
}
if (tries > max_tries)
puts("No valid input found");
else
printf("Valid input: %ld\n", number);
return EXIT_SUCCESS;
}
ADDED NOTE: If you change the base (the last parameter to strtol()) from 10 to zero, you'll get the additional feature that your code converts hexadecimal numbers and octal numbers (strings starting with 0x and 00 respectively) into integers.
I took #4386427 idea and just added codes to cover what it missed (leading spaces and + sign), I tested it many times and it is working perfectly in all possible cases.
#include<stdio.h>
#include <ctype.h>
#include <stdlib.h>
int validate_line (char *line);
int main(){
char line[256];
int y=0;
long x;
while (y<5){
printf("Please Insert X Value\n");
if (fgets(line, sizeof(line), stdin)){//return 0 if not execute
if (validate_line(line)>0){ // check if the string contains only numbers
x =strtol(line, NULL, 10); // change the authentic string to long and assign it
printf("This is x %d" , x);
break;
}
else if (validate_line(line)==-1){printf("You Have Not Inserted Any Number!.... ");}
else {printf("Invalid Input, Insert Integers Only.... ");}
}
y++;
if (y==5){printf("NO MORE RETRIES\n\n");}
else{printf("%d Retries Left\n\n", (5-y));}
}
return 0;}
int validate_line (char *line){
int returned_value =-1;
/*first remove spaces from the entire string*/
char *p_new = line;
char *p_old = line;
while (*p_old != '\0'){// loop as long as has not reached the end of string
*p_new = *p_old; // assign the current value the *line is pointing at to p
if (*p_new != ' '){p_new++;} // check if it is not a space , if so , increment p
p_old++;// increment p_old in every loop
}
*p_new = '\0'; // add terminator
if (*line== '+' || *line== '-'){line++;} // check if the first char is (-) or (+) sign to point to next place
while (*line != '\n'){
if (!(isdigit(*line))) {return 0;} // Illegal char found , will return 0 and stop because isdigit() returns 0 if the it finds non-digit
else if (isdigit(*line)){line++; returned_value=2;}//check next place and increment returned_value for the final result and judgment next.
}
return returned_value; // it will return -1 if there is no input at all because while loop has not executed, will return >0 if successful, 0 if invalid input
}
I have a function to read a text file with the following format
string int int
string int int
string int int
I want to write a function that will assign the values from the text file into variables, but there will also be some cases where the format of the text file will be
string int
string int
string int
In that case, I'd like to set the value of the last int variable to 1. My code I have so far works with the first example but I'm a bit stuck on getting the second scenario to work:
void readFile(LinkedList *inList, char* file)
{
char tempName[30];
int tempLoc, tempNum;
FILE* f;
f = fopen(file, "r");
if(f==NULL)
{
printf("Error: could not open file");
}
else
{
while (fscanf(f, "%s %d %d\n", tempName, &tempLoc, &tempNum) != EOF)
{
insertFirst (inList, tempName, tempLoc, tempNum);
}
}
}
In the second case, fscanf will return 2 instead of 3. So you can rewrite the code like this:
while (1) {
int ret = fscanf(f, "%s %d %d\n", tempName, &tempLoc, &tempNum);
if (ret == EOF) {
break;
}
if (ret == 2) {
tempNum = 1;
} else if (ret != 3) {
// line appear invalid, deal with the error
}
insertFirst (inList, tempName, tempLoc, tempNum);
}
A more hacky way would be to set tempNum to 1 before calling fscanf and just check for EOF as you did above. But I think the code above is clearer.
Edit: to avoid overflows, this would be better. The code would perform better but this is harder to write. Just like above, I did not write any code for the error conditions but you definitely want to handle them
char lineBuf[255];
while (fgets(lineBuf, sizeof(lineBuf), f) != NULL) {
int spaceIdx, ret;
const int len = strlen(lineBuf);
if (len == (sizeof(lineBuf) - 1) {
// line is too long - either your buf is too small and you should tell the user
// that its input is bad
// I recommend to treat this as an error
}
lineBuf[len - 1] = '\0'; // remove \n
--len; // update len, we've removed one character
if (isspace(*lineBuf)) {
// error, line should not start with a space
}
spaceIdx = strcspn(lineBuf, "\t ");
if (spaceIdx == len) {
// error, no space in this line
}
// Ok, we've found the space. Deal with the rest.
// Note that for this purpose, sscanf is a bit heavy handed (but makes the code
// simpler). You could do it with strtol.
// Also, the first space in the format string is important, so sscanf skips
// all the space at the beginning of the string. If your format requires only
// one space between fields, you can do sscanf(lineBuf + spaceIdx + 1, "%d %d"...
ret = sscanf(lineBuf + spaceIdx, " %d %d", &tempLoc, &tempNum);
if (0 == ret) {
// error, no ints
}
else if (1 == ret) {
tempNum = 1;
}
// at that point, you could copy the first part of lineBuf to tempName, but then
// you have to deal with a potential overflow (and spend time on an useless copy),
// so use lineBuf instead
lineBuf[spaceIdx] = '\0';
insertFirst (inList, lineBuf, tempLoc, tempNum);
}
This function is supposed to get a file of vectors. The first line
contains the dimension. All other line are in the form of
"P:3,5,2". The letter is P or N and the numbers are coordinates.
This function read a line each time it is being invoked and it saves the P/N char and the
coordinates into an array of double.
void readSamplesFile(FILE *sample_p, double result[])
{
if (dimension == 0)
{
fscanf(sample_p,"%lf",&dimension);
}
printf("dimentions: %lf\n",dimension);
printf("LINE \n");
int index;
for (index = 0; index<dimension; index++)
{
printf("%d",index);
fscanf(sample_p,"%lf%*[:,]",&result[index]);
printf("%lf",result[index]);
}
}
when i run it i get an endless loop. the dimension is read correctly but the
it prints
LINE
00.00000010.000000dimentions: 2.000000
endlessly. any ideas why?
hope i was clear
EDIT:
I've added the calling function:
void fillArray(FILE *sample_p,FILE *separators_p){
double coordinates[MAX_DIMENSION];
while (!feof(sample_p)){
readSamplesFile(sample_p,coordinates);
}
}
p.s.
fscanf is set to read : and , but to ignore them.
Neither 'P' nor 'N' is a valid double, nor are they ':' or ',', so the fscanf() fails. You should always check the return value from fscanf().
We can also debate whether you'd be better off using fgets() to read a line and sscanf() to parse it. Doing so avoids some issues; it is the way I'd code it automatically.
This code seems to work on the input file:
3
P:3,5,2
N:21.12,2.345e6,1.9132e-34
yielding the output:
dimension: 3.000000
LINE: P:3,5,2
P:offset=2:0=3(2):1=5(4):2=2(6):
LINE: N:21.12,2.345e6,1.9132e-34
N:offset=2:0=21.12(2):1=2.345e+06(8):2=1.9132e-34(16):
I'm still not keen on the (mis)use of a floating point dimension, but it works.
#include <stdio.h>
enum { MAX_DIMENSION = 6 };
enum { MAX_BUFFSIZE = 4096 };
static double dimension = 0.0;
static int get_dimension(FILE *fin)
{
char buffer[MAX_BUFFSIZE];
if (fgets(buffer, sizeof(buffer), fin) == 0)
return -1;
if (sscanf(buffer, "%lf", &dimension) != 1)
return -1;
printf("dimension: %lf\n", dimension);
return 0;
}
static int readSamplesFile(FILE *sample_p, double result[])
{
char buffer[MAX_BUFFSIZE];
if (fgets(buffer, sizeof(buffer), sample_p) == 0)
return -1;
printf("LINE: %s", buffer);
char c;
int offset;
if (sscanf(buffer, " %c:%n", &c, &offset) != 1)
return -1;
printf("%c:", c);
printf("offset=%d:", offset);
for (int index = 0; index < dimension; index++)
{
int newoff;
if (sscanf(&buffer[offset], "%lf%*[:,]%n", &result[index], &newoff) < 1)
return -1;
printf("%d=%g(%d):", index, result[index], offset);
offset += newoff;
}
putchar('\n');
return 0;
}
static void fillArray(FILE *sample_p)
{
double coordinates[MAX_DIMENSION];
while (readSamplesFile(sample_p, coordinates) == 0)
;
}
int main(void)
{
if (get_dimension(stdin) == 0)
fillArray(stdin);
return 0;
}
Note that the fillArray() function, as written, does not do anything with the line of data. There is no checking that the dimension specified is positive and not greater than MAX_DIMENSION (that would go in get_dimension()). It feels cleaner to separate get_dimension() into a separate function than to hide it inside readSampleFile(). There is an argument that readSampleFile() should be renamed readSampleLine() since it does only process one line at a time, not a whole file at a time.
The use of the %n format specifier is a little tricky, but the code needs to know where to resume reading the buffer on the next cycle.