Text processing. (Chapter 23)

Overview

Application domains
Strings
I/O
Maps
Regular expressions

Stroustrup/PPP - Nov'13

Now you know the basics

Really! Congratulations!
Don’t get stuck with a sterile

Text processing

“all we know can be represented as text”
And often is
Books,

String overview

Strings
std::string

s.size()
s1==s2
C-style string (zero-terminated array of char)
or
strlen(s)
strcmp(s1,s2)==0
std::basic_string, e.g. Unicode

C++11 String Conversion

In , for numerical values
For example:
string s1 = to_string(12.333); //

String conversion

We can write a simple to_string() for any type that

C++11 String Conversion

Part of , for numerical destinations
For example:
string s1 =

String conversion

We can write a simple from_string() for any type that

General stream conversion

 template
Target to(Source arg)
{
std::stringstream ss;
Target result;
if (!(ss

I/O overview

Stroustrup/PPP - Nov'13

Map overview

Associative containers

Map overview

Stroustrup/PPP - Nov'13

A problem: Read a ZIP code

U.S. state abbreviation and ZIP code
two

A problem: Read a ZIP code

Problems with simple solution 
It’s verbose (4

TX77845-1234

1st try: wwddddd
2nd (remember -12324): wwddddd-dddd
What’s “special”?
3rd: \w\w\d\d\d\d\d-\d\d\d\d
4th (make counts explicit): \w2\d5-\d4
5th (and “special”): \w{2}\d{5}-\d{4}
But

#include
#include
#include
using namespace std;
int main()
{
ifstream in("file.txt"); // input file
if (!in)

 
int lineno = 0;
string line; // input buffer
while (getline(in,line)) {
++lineno;
smatch matches; // matched

Results

Input: address TX77845
ffff tx 77843 asasasaa
ggg TX3456-23456
howdy
zzz TX23456-3456sss ggg TX33456-1234
cvzcv TX77845-1234 sdsas
xxxTx77845xxx
TX12345-123456
Output: pattern:

Regular expression syntax

Regular expressions have a thorough theoretical foundation based on

Searching vs. matching

Searching for a string that matches a regular expression

Table grabbed from the web

KLASSE ANTAL DRENGE ANTAL PIGER ELEVER IALT
0A 12 11 23
1A 7 8 15
1B 4 11 15
2A 10 13 23
3A 10 12 22
4A 7 7 14
4B 10 5 15
5A 19 8 27
6A 10 9 19
6B 9 10 19
7A 7 19 26
7G 3 5 8
7I 7 3 10
8A 10 16 26
9A 12 15 27
0MO 3 2 5
0P1 1 1 2
0P2 0 5 5
10B 4 4 8
10CE 0 1 1
1MO 8 5 13
2CE 8 5 13
3DCE 3 3 6
4MO 4 1 5
6CE 3 4 7
8CE 4 4 8
9CE 4 9 13
REST 5 6 11
Alle

Describe rows

Header line
Regular expression: ^[\w ]+( [\w ]+)*$
As string literal: "^[\\w ]+( [\\w ]+)*$"
Other lines
Regular

Simple layout check

int main()
{
ifstream in("table.txt"); // input file
if (!in) error("no input file\n");
string

Simple layout check

int main()
{
// … open files, define patterns …
if (getline(in,line))

Validate table

int boys = 0; // column totals
int girls = 0;
while (getline(in,line))