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I have a software that reads from a file. Each object in the software takes 7 inputs viz.

string string string float string float int

I have an input file. It contains a number of input values. If input for one object is like:

hss cscf "serving cscf" 32.5 ims 112.134 124

(Note: when an object's variable needs multi word string, I used "....", for single word string, it is without quotes)

How can I read it using ifstream? (I searched google but didn't find.)

I tried to read entire line using getline and but again got stuck when it came to find out whether its a single word or multi word input! I thought to read a line and then search char by char. If its '"', I know its a multi word. But I stuck when it comes to an integer or float. For char, you can use

if(line[i]>='a'&&line[i]<='z')

but how to go ahead when integer or float is the next value?

Please give some suggestions for this.

Aakash Goyal
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  • you couldn't [google how to use ifstream](http://stackoverflow.com/questions/7443787/using-c-ifstream-extraction-operator-to-read-formatted-data-from-a-file)? – gbjbaanb Aug 13 '13 at 12:09
  • By not able to find how to use ifstream on google means I was unable to search how to read above mentioned input format. If they are all single words, I know how to read. If they are in separate line, I know how to read. But how to read when you dont know whether you will counter a multi word or single word for your next input is what I couldn't find and asked. – Aakash Goyal Aug 14 '13 at 04:21

1 Answers1

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You can differentiate numbers from words by looking at the characters within them. Basically, if a word contains exclusively [0-9.], you can assume it's a number.

In the same way, if an assumed number contains only [0-9], it's an integer. Otherwise, it's a float.

Beware of edge cases:

  • Cultures matter. In French, for example, you don't write 19.95, but 19,95. Even worse, the number 1 582.16 can be written 1582.16, 1,582.16, 1.582,16, etc., depending on the culture.

  • How do you escape strings? What if a multiword string contains a quote character?

  • Unicode can make things difficult, since unicode characters can be normalized and decomposed.

  • What if, one day, you need to have a word which has only digits, but still be interpreted as a word?

Side note: couldn't you reuse an existent format, like JSON, with already written and tested parsers? See also: How are new file formats constructed?

Community
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Arseni Mourzenko
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  • if using an existing format isn't possible then using existing parser generator libraries might be – jk. Aug 13 '13 at 12:20