convert string of ints and floats to a float array in C

Question

what I'm trying to do is to send a string over the network. the point is that the server which receives the string must make the sum of all the numbers and send it back. so i think the easiest way is to take the string and put it in a float array (it does not matter if ints get in there aswell, since the final sum will be a float number).

unfortunately i have no idea how to do that, or more exactly, how to approach it. how do i take the numbers 1 by 1 from a string (let's say, each number is separated by a space)? there must be some function but i can't find it.

the language is plain C under unix.

unwind · Accepted Answer · 2014-03-11 10:05:47Z

4

Use strtod() to convert the first number in the string to double. Add that to your sum, then use the endptr return value argument to figure out if you need to convert another, and if so from where. Iterate until the entire string has been processed.

The prototype for strtod() is:

double strtod(const char *nptr, char **endptr);

Also note that you can run into precision issues when treating integers as floating-point.

edited Mar 11, 2014 at 10:05

answered Mar 10, 2014 at 16:39

unwind

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2 Comments

Emmet Over a year ago

IMO, this is the best proposed solution. The other solutions all use “evil” functions that modify their arguments or maintain internal state.

icarus Over a year ago

this clearly looks like the easiest solution and it's exactly what i wanted. i argued a bit with it because i didn't realize where the endpointer should come from, but alas i made it work. thank you.

radomaj · Accepted Answer · 2014-03-10 16:40:42Z

1

You can use fscanf to read from a stream, just like you would use scanf to read from stdin.

answered Mar 10, 2014 at 16:40

radomaj

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Comments

Arjun Sreedharan · Accepted Answer · 2014-03-10 16:54:00Z

0

You can use strtok to split your string and atof to convert it to float.

char* p;
float farr[100];
int i = 0;
//str is your incoming string
p = strtok(str," ");
while (p != NULL)
{
    farr[i] = atof(p);
    p = strtok(NULL, " ");
}

I just ran it in an online compiler - http://ideone.com/b3PNTr

edited Mar 10, 2014 at 16:54

answered Mar 10, 2014 at 16:44

Arjun Sreedharan

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Comments

LearningC · Accepted Answer · 2014-03-10 17:03:50Z

-1

you can use sscanf() to read the formatted input from a string.
you can use something like

string=strtok(input," ")
while(string!=NULL)
{ sscanf(string,"%f",&a[i]);
  i++;
string=strtok(NULL," ");
}

inside a loop. you can use even atof() instead of using sscanf() with %f.

edited Mar 10, 2014 at 17:03

answered Mar 10, 2014 at 16:40

LearningC

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3 Comments

Emmet Over a year ago

You left out an 's' on sscanf() in your example.

unwind Over a year ago

This doesn't say anything about how to skip the beginning of string to get to the next number.

LearningC Over a year ago

@unwind ya right. now i have specified how to get the string.

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