c++ regular expression matching whole line - c++

Question

I am trying to parse a text file the contains numeric data. I have a lot of lines that look like
129.3 72.7 121.6 173.6 203.3 120.7 40.5 79.2 94.0 123.2 165.8 178.8 135.5 78.5 66.2
but the length of the lines vary. Each line is also preceded by a few spaces.
I would like to use regular expressions to parse the line and place each number into an array that I can then manipulate later.
Using
std::getline(is, line);
std::tr1::regex rx("[0-9-\.]+");
std::tr1::cmatch res;
std::tr1::regex_search(line.c_str(), res, rx);
only matches the first number. If instead I use line anchors such as
"^[0-9-\.]+$"
"^[0-9-\.]+"
I get no matches and
"[0-9-\.]+$"
just matches the last number. So I am probably doing something wrong. Thanks for any help.

Answer 1

Um, pseudocode
for str in strtok(input string)
vector[index] = convert str to float
Here's an example using lots of stream magic: Split a string in C++?
Here's an example using a vector:
Splitting a string by whitespace in c++
But plain old strtok is probably easiest:
http://www.cplusplus.com/reference/clibrary/cstring/strtok/
in which case you'll get something like
Vector flts = // create it
for(int ix=0, char * cp; cp = strtok(str," "); ix++){
flts[ix] = atof(cp);
}
Now, that's very C like because I'm out of practice for C++, but the key point here is that by trying to use regex, you make it overcomplicated.

Answer 2

You need to include the space between the numbers in your match to match the whole line.
BTW, take a look at C++ tokenize a string using a regular expression to see a rather closely related answer.
You really shouldn't be using arrays here, use the standard containers for safety, convenience and sanity of anyone who has to look at this code later.

Answer 3

I looks like the regex has a small issue:
"[0-9-\.]+"
should be more like:
"[0-9\.]"

Answer 4

your regex might be incorrect, you should try:
[0-9\.]+
also keep in mind that std::tr1::cmatch returns an arrays of matches, i.e. res[2] contains 72.7
Using egrep you can experiment a bit:
egrep "[0-9-\.]+" /tmp/x
egrep: Invalid range end
but
egrep "^[0-9\.]+" /tmp/x
matches only
129.3
and
egrep "[0-9\.]+" /tmp/x
matches all
129.3 72.7 121.6 173.6 203.3 120.7 40.5 79.2 94.0 123.2 165.8 178.8 135.5 78.5 66.2
you don't need ^ in front because it matches a null character at the start of the string, i.e. you gen only the first sequence of numbers.
you don't need $ because it matches only the null character at the end, thus you get only the last sequence of numbers
you need + since you want to get all the matching atoms of type [0-9\.].
Also you can get a short guide regex matching in any unix system by issueing
man -S 7 regex
p.s. /tmp/x is a file with the line that is provided in the question.