The goal of this program is to create a function which reads in a single string, user typed, command (ultimately for program to be used in conjunction with a robot) which consists of an unknown command word(stored and printed as command), and an unknown number of decimal parameters(the quantity is stored and printed as num, and the parameters are to be stored as float values in the array params). In the User input, the command and parameters will be separated by spaces. I believe my issue is with the atof function when I go to extract the decimal values from the string. What am I doing wrong? Thank you for the help!
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void func(char *input, char *command, int *num, float *params);
int main()
{
char input[40]={};
char command[40]={};
int num;
float params[10];
printf("Please enter your command: ");
gets(input);
func(input,command,&num,params);
printf("\n\nInput: %s",input);
printf("\nCommand: %s",command);
printf("\n# of parameters: %d",num);
printf("\nParameters: %f\n\n",params);
return 0;
}
void func(char *input, char *command, int *num, float *params)
{
int i=0, k=0, j=0, l=0;
int n=0;
while(input[i]!=32)
{
command[i]=input[i];
i++;
}
for (k=0; k<40;k++)
{
if ((input[k]==32)&&(input[k-1]!=32))
{
n++;
}
}
*num=n;
while (j<n)
{
for (l=0;l<40;l++)
{
if((input[l-1]==32)&&(input[l]!=32))
{
params[j]=atof(input[l]);
j++;
}
}
}
}
A Sample Output Screen:
Please enter your command: Move 10 -10
Input: Move 10 -10
Command: Move
# of parameters: 2
Parameters: 0.000000
The Parameters output should, ideally, read "10 -10" for the output. Thanks!
Change atof(input[l]) to atof(input + l). input[l] is single char but you want to get substring from l position. See also strtod() function.
Other people have already remarked the problem in your code, but may I suggest that you have a look at strtod() instead?
While both atof() and strtod() discard spaces at the start for you (so you don't need to do it manually), strtod() will point you to the end of the number, so that you know where to continue:
while(j < MAX_PARAMS) // avoid a buffer overflow via this check
{
params[j] = strtod(ptr, &end); // `end` is where your number ends
if(ptr == end) // if end == ptr, input wasn't a number (say, if there are none left)
break;
// input was a number, so ...
ptr = end; // continue at end for next iteration
j++; // increment number of params
}
Do note that the above solution does not differentiate between invalid arguments (say, foo instead of 3.5) and missing ones (because we've hit the last argument). You can check for that by doing this: if(!str[strspn(str, " \t\v\r\n\f")]) --- this checks if we're at the end of string (but allowing trailing whitespace). See the second side-note for what it does.
SIDE-NOTES:
You can use ' ' instead of 32 to check for space; this has two advantages:
It is clearer to the reader (it's very clear that it's a whitespace, instead of "some magic number that happens to have meaning")
It works in non-ASCII encodings (and the standard allows other encodings, though ASCII is by far the most popular; one common encoding is EBCDIC)
For future reference, this trick can help you skip whitespace: ptr += strspn(ptr, " \t\v\r\n\f");. strspn returns the number of characters at the start of the string that match the set (in this case, one of " \t\v\r\n"). Check documentation for more info.
Example for strspn: strspn("abbcbaa", "ab"); returns 3 because you have aab (which match) before c (which doesn't).
you are trying to convert a char into a float,
params[j]=atof(input[l]);
you should get the entire word(substring) of the float.
Example, "12.01" a null terminated string with 5 characters and pass it to atof, atof("12.01") and it will return a double of 12.01.
so, you should first extract the string for each float parameter and pass it to atof
Avoid comparing character to ascii value, rather you could have use ' ' (space) directly.
Instead of using for loop with a fixed size, you can use strlen() or strnlen() to find the length of the input string.
Related
How can I split character and variable in 1 line?
Example
INPUT
car1900food2900ram800
OUTPUT
car 1900
food 2900
ram 800
Code
char namax[25];
int hargax;
scanf ("%s%s",&namax,&hargax);
printf ("%s %s",namax,hargax);
If I use code like that, I need double enter or space for make output. How can I split without that?
You should be able to use code like this to read one name and number:
if (scanf("%24[a-zA-Z]%d", namax, &hargax) == 2)
…got name and number OK…
else
…some sort of problem to be reported and handled…
You would need to wrap that in a loop of some sort in order to get three pairs of values. Note that using &namax as an argument to scanf() is technically wrong. The %s, %c and %[…] (scan set) notations all expect a char * argument, but you are passing a char (*)[25] which is quite different. A fortuitous coincidence means you usually get away with the abuse, but it is still not correct and omitting the & is easy (and correct).
You can find details about scan sets etc in the POSIX specification of scanf().
You should consider reading a whole line of input with fgets() or POSIX
getline(), and then processing the resulting string with sscanf(). This makes error reporting and error recovery easier. See also How to use sscanf() in loops.
Since you are asking this question which is actually easy, I presume you are somewhat a beginner in C programming. So instead of trying to split the input itself during the input which seems to be a bit too complicated for someone who's new to C programming, I would suggest something simpler(not efficient when you take memory into account).
Just accept the entire input as a String. Then check the string internally to check for digits and alphabets. I have used ASCII values of them to check. If you find an alphabet followed by a digit, print out the part of string from the last such occurrence till the current point. And while printing this do the same with just a slight tweak with the extracted sub-part, i.e, instead of checking for number followed by letter, check for letter followed by digit, and at that point print as many number of spaces as needed.
just so that you know:
ASCII value of digits (0-9) => 48 to 57
ASCII value of uppercase alphabet (A-Z) => 65 to 90
ASCII value of lowercase alphabets (a-z)
=> 97 to 122
Here is the code:
#include<stdio.h>
#include<string.h>
int main() {
char s[100];
int i, len, j, k = 0, x;
printf("\nenter the string:");
scanf("%s",s);
len = strlen(s);
for(i = 0; i < len; i++){
if(((int)s[i]>=48)&&((int)s[i]<=57)) {
if((((int)s[i+1]>=65)&&((int)s[i+1]<=90))||(((int)s[i+1]>=97)&&((int)s[i+1]<=122))||(i==len-1)) {
for(j = k; j < i+1; j++) {
if(((int)s[j]>=48)&&((int)s[j]<=57)) {
if((((int)s[j-1]>=65)&&((int)s[j-1]<=90))||(((int)s[j-1]>=97)&&((int)s[j-1]<=122))) {
printf("\t");
}
}
printf("%c",s[j]);
}
printf("\n");
k = i + 1;
}
}
}
return(0);
}
the output:
enter the string: car1900food2900ram800
car 1900
food 2900
ram 800
In addition to using a character class to include the characters to read as a string, you can also use the character class to exclude digits which would allow you to scan forward in the string until the next digit is found, taking all characters as your name and then reading the digits as an integer. You can then determine the number of characters consumed so far using the "%n" format specifier and use the resulting number of characters to offset your next read within the line, e.g.
char namax[MAXNM],
*p = buf;
int hargax,
off = 0;
while (sscanf (p, "%24[^0-9]%d%n", namax, &hargax, &off) == 2) {
printf ("%-24s %d\n", namax, hargax);
p += off;
}
Note how the sscanf format string will read up to 24 character that are not digits as namax and then the integer that follows as hargax storing the number of characters consumed in off which is then applied to the pointer p to advance within the buffer in preparation for your next parse with sscanf.
Putting it altogether in a short example, you could do:
#include <stdio.h>
#define MAXNM 25
#define MAXC 1024
int main (void) {
char buf[MAXC] = "";
while (fgets (buf, MAXC, stdin)) {
char namax[MAXNM],
*p = buf;
int hargax,
off = 0;
while (sscanf (p, "%24[^0-9]%d%n", namax, &hargax, &off) == 2) {
printf ("%-24s %d\n", namax, hargax);
p += off;
}
}
}
Example Use/Output
$ echo "car1900food2900ram800" | ./bin/fgetssscanf
car 1900
food 2900
ram 800
I'm using atoi to convert a string integer value into integer.
But first I wanted to test different cases of the function so I have used the following code
#include <stdio.h>
int main(void)
{
char *a ="01e";
char *b = "0e1";
char *c= "e01";
int e=0,f=0,g=0;
e=atoi(a);
f=atoi(b);
g=atoi(c);
printf("e= %d f= %d g=%d ",e,f,g);
return 0;
}
this code returns e= 1 f= 0 g=0
I don't get why it returns 1 for "01e"
that's because atoi is an unsafe and obsolete function to parse integers.
It parses & stops when a non-digit is encountered, even if the text is globally not a number.
If the first encountered char is not a space or a digit (or a plus/minus sign), it just returns 0
Good luck figuring out if user input is valid with those (at least scanf-type functions are able to return 0 or 1 whether the string cannot be parsed at all as an integer, even if they have the same behaviour with strings starting with integers) ...
It's safer to use functions such as strtol which checks that the whole string is a number, and are even able to tell you from which character it is invalid when parsing with the proper options set.
Example of usage:
const char *string_as_number = "01e";
char *temp;
long value = strtol(string_as_number,&temp,10); // using base 10
if (temp != string_as_number && *temp == '\0')
{
// okay, string is not empty (or not only spaces) & properly parsed till the end as an integer number: we can trust "value"
}
else
{
printf("Cannot parse string: junk chars found at %s\n",temp);
}
You are missing an opportunity: Write your own atoi. Call it Input2Integer or something other than atoi.
int Input2Integer( Str )
Note, you have a pointer to a string and you will need to establish when to start, how to calculate the result and when to end.
First: Set return value to zero.
Second: Loop over string while it is not null '\0'.
Third: return when the input character is not a valid digit.
Fourth: modify the return value based on the valid input character.
Then come back and explain why atoi works the way it does. You will learn. We will smile.
so i've been writing a program that convert a decimal number to it's boolean representation but every time i compile the return value which is a string show additional characters like p┐ here is the program
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void main (void)
{
signed char str[256];
int dec,rest;
int i = -1;
int j;
printf ("write a decimal number : ");
scanf ("%d",&dec);
do
{
rest = dec % 2;
dec/= 2;
for (j=i;j>-1;--j)
str[j+1]=str[j];
str[0]=rest+48;
++i;
} while (dec!=0);
printf ("the binary representation of this number is %s",str);
}
the output :
write a decimal number : 156
the binary representation of this number is 10011100p┐
i don't know if im missing something but i will be grateful if you guys help me
In C and C++, strings are null-terminated, this means that every valid string must end with a character with code 0. This character tells every function that is dealing with this string that it is in fact over.
In your program you create a string, signed char str[256]; and it is initially filled with random data; this means that you reserved space for 256 characters and they are all garbage, but the system does not know they are invalid. Try printing this string and see what happens.
In order to actually tell the system that your string is over after say, 8 characters, the 9th character hast to be the NUL character, or simply 0. In your code you can do it in two ways:
after the loop, assign str[i] = 0, or (even simpler)
initialize the string as signed char str[256]={0};, whiche creates the storage and fills it with nulls; after writing to the string you can be sure that the character after the last one you've written will be a NUL.
At the end of your do {} while () loop, you need to set the character after the last character in your string to 0. This is the array index of the last character you want (i) plus one. This lets printf know where your string ends. (Otherwise, how could it know?)
initialize the str variable to NUL.
void main (void)
{
signed char str[256];
int dec,rest;
int i = -1;
int j;
memset( str, '\0', sizeof(str) );
printf ("write a decimal number : ");
scanf ("%d",&dec);
do
{
rest = dec % 2;
dec/= 2;
for (j=i;j>-1;--j)
str[j+1]=str[j];
str[0]=rest+48;
++i;
} while (dec!=0);
printf ("the binary representation of this number is %s",str);
}
First of all let me ask for your forgiveness if this is too trivial, I am not a C developer, usually I program in Fortran.
I am in need to read some columnated text files. The problem I have is that some columns can have blank space (non filled value) or not fully filed field.
Let me use a short example of the problem. Lets say I have a generator program like:
#include <stdio.h>
#include <stdlib.h>
int main(){
printf("xxxx%4d%4.2f\n",99,3.14);
}
When I execute this program I get:
$ ./t1
xxxx 993.14
If I get it into a text file and try to read using (e.g.) sscanf with the code:
#include <stdio.h>
#include <stdlib.h>
int main() {
char *fmt = "%*4c%4d%4f";
char *line = "xxxx 993.14";
int ival;
float fval;
sscanf(line,fmt,&ival,&fval);
printf(">>>>%d|%f\n",ival,fval);
}
The result is:
$ ./t2
>>>>993|0.140000
What is the problem here? The sscanf seems to think that all space is meaningless and should be discarded. So the "%4c" does what it is meant to be, it counts 4 characters without discarding any blank space and discards everything due to "". Next the %4d start skipping all blank spaces and start count the 4 characters of the field upon finding the first valid character for the conversion. So the value, meant to be 99 becomes 993, and the 3.14 becomes 0.14.
In Fortran the reading code would be:
program t3
implicit none
integer :: ival
real :: fval
character(len=30) :: fmt="(4x,i4,f4.0)"
character(len=30) :: line="xxxx 993.14"
read(line,fmt) ival, fval
write(*,"('>>>>',i4,'|',f4.2)") ival,fval
end program t3
and the result would be:
$ ./t3
>>>> 99|3.14
That is, the format specification states the field width and nothing is discarding in conversion, except if instructed to by the "nX" specification.
Some final remarks to help the helpers:
The format to be read is an international standard and there is no
way to change it.
The number of existing files is to big to think of intervention or
format change.
It is not a CSV or similar format.
The code has to be in C for integration in a free software package.
Sorry to be too long, trying to state the problem as completely as possible.
The question is: Is there a way to tell sscanf to not skip the blank spaces? If not, is there a simple way to do it in C or it will be necessary write an specialized parser for each record type?
Thank you in advance.
When reading fixed-length fields with sscanf, it is best to parse the values as character strings (which you could do a number of ways), and then perform independent conversion of each of the fields. This allows you to handle conversion/error detection on a per-field basis. For example, you could use a format string of:
char *fmt = "%*4s%2[^0-9]%s";
which would read/discard the 4 leading characters, then read 2-chars as your integer, followed by the remainder of line (or up until the next whitespace) as a string containing your float value.
To handle the storage and parsing of line as fixed length fields, you could use temporary character arrays to hold each of the strings and then use sscanf to fill them much as you have attempted to do with the integer and float directly. e.g.:
char istr[8] = {0};
char fstr[16] = {0};
...
sscanf (line,fmt,istr,fstr);
(note: you could use minimum storage of istr[3] and fstr[7] in this given case, adjust the storage length as required, but providing space for the nul-terminating character)
You can then use strtol and strtof to provide conversion with error checking on each value. For example:
errno = 0;
if ((ival = (int)strtol (istr, NULL, 10)) == 0 && errno)
fprintf (stderr, "error: integer conversion failed.\n");
/* underflow/overflow checks omitted */
and
errno = 0;
if ((fval = strtof (fstr, NULL)) == 0 && errno)
fprintf (stderr, "error: integer conversion failed.\n");
/* nan and inf checks omitted */
Putting all the pieces together in you example, you could use something like:
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
int main() {
char *fmt = "%*4s%2[^0-9]%s";
char *line = "xxxx 993.14";
char istr[8] = {0};
char fstr[16] = {0};
int ival;
float fval;
sscanf (line,fmt,istr,fstr);
errno = 0;
if ((ival = (int)strtol (istr, NULL, 10)) == 0 && errno)
fprintf (stderr, "error: integer conversion failed.\n");
/* underflow/overflow checks omitted */
errno = 0;
if ((fval = strtof (fstr, NULL)) == 0 && errno)
fprintf (stderr, "error: integer conversion failed.\n");
/* nan and inf checks omitted */
printf(">>>>%d|%6.2f\n",ival,fval);
return 0;
}
Example/Output
$ >>>>0|993.14
*scanf() is not designed to handle fixed column width with non-intervening white-space.
With sscanf(), to not skip spaces, code must use "%c", "%n", "%[]" as all other specifiers skip leading white-space and those skipped characters do not contribute to a width limit.
To scan the printed line, which in now in buffer, take advantage that the only use of '\n' is at the end of the line.
char str_int[5];
char str_float[5];
int n = 0;
sscanf(buffer, "%*4c%4[^\n]%4[^\n]%n", str_int, str_float, &n);
if (n != 12 || buffer[n] != '\n') Fail();
// Now convert str_int, str_float as needed.
Another way to use sscanf() would be to parse buffer as
int ival;
float fval;
if (strlen(buffer) != 13) Fail();
if (sscanf(&buffer[8], "%f", &fval) != 1) Fail();
buffer[8] = '\0';
if (sscanf(&buffer[4], "%d", &ival) != 1) Fail();
Note: The 4s in the below do not specified the output width as 4 characters. 4 is the minimum width to print.
printf("xxxx%4d%4.2f\n",ival, fval);
Code could use the following to detect problems.
if (13 != printf("xxxx%4d%4.2f\n",ival, fval)) Fail();
Watch out for
printf("xxxx%4d%4.2f\n",123, 9.995000001f); // "xxxx 12310.00\n"
First off, I dunno. There might be some way to wrangle sscanf to recognize the whitespace towards your integer count. But I just don't think scanf was made for this sort of format in mind. The tool's trying to be smart of helpful and it's biting you in the ass.
But if it's columnated data and you know the position of the various fields, there's a really easy work around. Just extract the field you want.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char** argv)
{
char line[] = "xxxx 893.14";
char tmp[100];
int thatDamnNumber;
float myfloatykins;
//Get that field
memcpy(tmp, line+4, 4);
sscanf(tmp, "%d", &thatDamnNumber);
//Kill that field so it doesn't goober-up the float
memset(line+4, ' ', 4);
sscanf(line, "%*4c%f", &myfloatykins);
printf("%d %f\n", thatDamnNumber, myfloatykins);
return 0;
}
If there is a lot of this, you could make some generalized functions: integerExtract(int positionStart, int sizeInCharacters), floatExtract(), etc.
If each element is of fixed width you don't really need scanf(), try this
char copy[5];
const char *line = "xxxx 993.14";
int ival;
float fval;
copy[0] = line[4];
copy[1] = line[5];
copy[2] = line[6];
copy[3] = line[7];
copy[4] = '\0'; // nul terminate for `atoi' to work
ival = atoi(copy);
fval = atof(&line[8]);
fprintf(stdout, "%d -- %f\n", ival, fval);
If you want (probably should) you can use strtol() instead of atoi() and strtof() instead of atof() to check for malformed data.
Both these functions take a parameter to store the unconverted/invalid characters, you can check the passed pointer in order to verify that there was a problem with conversion.
Or if you really want scanf() do the same, capture the integer + whitespaces to a char array and then convert it to int later, like this
char integer[5];
const char *line = "xxxx 993.14";
int ival;
float fval;
if (sscanf(line, "%*4c%4[0-9 ]%f", integer, &fval) != 2)
return -1;
ival = atoi(integer);
fprintf(stdout, "%d -- %f\n", ival, fval);
The format "%*4c%4[0-9 ]%f" will
Skip the first four characters including white spaces.
Scan the next four characters if they consist only of digits or white spaces.
Scan the rest of the input string searching for a matching float value.
I am posting what I think is a final conclusion from the answers I have got so far and from other sources.
What is a very trivial task in Fortran is not a so trivial task in other languages. I guess — not sure — that the same task could be as easy as in Fortran in other languages. I think that Cobol, Pascal, PL/I and others from the time of punched card probably could be trivial.
I think that most languages nowadays are more comfortable with different data structure and inherited its I/O structure from C. I think that Java, Python, Perl(?) and others could serve as examples.
From what I saw in this thread there are two main problems to read / convert fixed column length text data with C.
The first problem is that, as Philip said in his answer: “The tool’s trying to be smart of helpful and it’s biting you in the ass.” Quite right! The point is that it seems that C text I/O thinks that “white space” is something like a NULL character and should be thrown away, completely disregarding any information of the start of field. The only exception to that seems to be the %nc that get exactly n chars, even blanks.
The second problem is that the conversion “tag” (how is that called?) %nf will keep converting while it finds a valid character, even if you say stop at the 4th character.
If we join those two problems with a field completely filled with white space, depending on the conversion tool used, it throws an error or keeps going madly looking for something meaningful.
At the end of the day, it seems that the only way is to extract the field length to another memory area, dynamically allocated or not (we can have an area for each column length), and try to parse this separate area, taking into account the possibility of a full white space area to cache the error.
I need to limit the input from a user to only positive values, and count the number of digits in that number. The user will only type in a (+/-) whole number up to 9 characters long.
I'm only allowed to use the scanf function and for, while, or do-while loops.(I saw in similar questions how to do this using getchar, but I can only use scanf). I'm not allowed to use arrays, or any other library besides stdio.h and math.h
I know that if I write:
n=scanf("%c%c%c%c%c",&a,&b,&c,&e,&f);
n will count the number of successful scanf conversions.
The problem i'm having is that when I define the input with char, it does everything I want except that the user MUST enter 5 characters. So if the user wants to input "55" he has to press "5" "5" "enter" "enter" "enter".
I need the program to move on after the first "enter" but also be flexible to receive a number up to 9 digits long.
again, I can't use getchar or anything fancy. Just the really basic stuff in C that you learn in the first 2 weeks.
Use scanf to read the number into a long int , then use a for loop with a /10 to count the number of digits
What do you want the program to do in case of a -ve number being entered?
#include<stdio.h>
int main()
{
long int a;
int b;
do
{
scanf ("%ld",&a);
if(a<0)
printf ("invalid input");
}while(a<0);
for(b=0;a!=0;b++,a=a/10);
printf("%d",b);
}
(does not handle -ve numbers specially)
Something like
#include <stdio.h>
int main(void)
{
char buffer[10] = { 0 };
size_t len;
scanf("%9[0-9]", buffer);
for(len = 0; buffer[len] != 0; len++) ;
printf("%zu '%s'\n", len, buffer);
return 0;
}
works, but I don't know if it fits your need.
EDIT (bits of explanation)
You can replace size_t with int (or unsigned int), though size_t is better. If you do, use %d or %u instead of %zu.
The basic idea is to exploit a feature of the format of scanf; the 9[0-9] says the input is a sequence of up to 9 char in the given set i.e. the digits from 0 to 9.
The for(...) is just a way to count char, a simple implementation of a strlen. Then we print the result.
The approach I would take would be the following.
Loops are allowed, so go ahead and set one up.
You need to have a variable somewhere that will keep track of what the current number is.
Think about typing out a number, one character at a time. What needs to happen to the current_number variable?
You need to stop the loop if a return key has been pressed.
Something like this should do for starters, but I'll leave the rest up to you, specifically what return_check(ch), update_state(current_val) and char_to_int(ch) looks like. Also note that rather than use a function, feel free to put your own function directly into the code.
int current_val=0;
int num_digits=0;
char ch="\0"
for (num_digits=0;return_check(ch) && num_digits<=9;num_digits++)
{
fscanf("%c");
current_val=update_state(current_val);
current_val=current_val+char_to_int(ch);
}
As for the logic in update_state(), think about what happens, one character at a time, if a user types in a number, like 123456789. How is current_val different from a 1 to a 12, and a 12 to a 123.
Can you wrap a loop around it, something like (I don't know if all of the syntax is right):
const int max_size=9
int n=0; //counter for number of chars entered
char a[max_size-1];
do {
scanf(%c,&a[n]);
n++;
} while (a[n] != '\r' && n<max_size)