boost regex not matching?

Question

I am trying to follow the example here:

http://www.boost.org/doc/libs/1_31_0/libs/regex/doc/syntax.html

I want to match lines of this form:

[ foo77 ]

which should be simple enough, I tried a code snippet like this:

boost::regex rx("^\[ (.+) \]");

boost::cmatch what;
if (boost::regex_match(line.c_str(), what, rx)) std::cout << line << std::endl;

but I am not matching those lines. I tried the following variant expressions:

"^\[[:space:]+(.+)[:space:]+\]$" //matches nothing
"^\[[:space:]+(.+)[:space:]+\]$" //matches other lines but not the ones I want.

what am I doing wrong?

Fast guess: You might have to escape the '\'. In your case: boost::regex rx("^\\[ (.+) \\]"); — tgmath
– tgmath, Commented Feb 13, 2014 at 14:15

jfly · Accepted Answer · 2014-02-13 14:28:24Z

1

change boost::regex rx("^\[ (.+) \]"); to boost::regex rx("^\\[ (.+) \\]");, it will work fine, the compiler should warn about the unrecognized character escape sequence.

edited Feb 13, 2014 at 14:28

answered Feb 13, 2014 at 14:18

jfly

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Comments

Praetorian · Accepted Answer · 2014-02-13 14:20:28Z

0

You need to escape the \ within the regular expression, otherwise your compiler will consider "\[" as an (invalid) escape sequence.

boost::regex rx("^\\[ (.+) \\]");

A better solution is to use raw string literals.

boost::regex rx(R"(^\[ (.+) \])");

answered Feb 13, 2014 at 14:20

Praetorian

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2 Comments

James Kanze Over a year ago

Raw string literals are only available in C++11. And if he had C++11, he'd be using std::regex instead of Boost (presumably, at least).

Praetorian Over a year ago

@James Unless he's using gcc, std::regex doesn't really work in versions prior to 4.9.

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