How to do std::string indexof in C++ that returns index of matching string?

Question

I'm looking for a string indexof function from the std namespace that returns an integer of a matching string similar to the java function of the same name. Something like:

std::string word = "bob";
int matchIndex = getAString().indexOf( word );

where getAString() is defined like this:

std::string getAString() { ... }

Andrew Hare · Accepted Answer · 2009-03-16T18:41:56.037

34

Try the find function.

Here is the example from the article I linked:

 string str1( "Alpha Beta Gamma Delta" );
 string::size_type loc = str1.find( "Omega", 0 );
 if( loc != string::npos ) {
   cout << "Found Omega at " << loc << endl;
 } else {
   cout << "Didn't find Omega" << endl;
 }

edited Mar 16 '09 at 18:41

answered Mar 16 '09 at 17:58

Andrew Hare

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1

Is there a function for actually finding the _index_ at which the substring begins? I could subtract the beginning iterator, but is that necessary? – Arnav Borborah Oct 26 '17 at 14:16
@ArnavBorborah `find` returns the index. The unsigned integer type `string::size_type` is just there to guarantee that the result of `find` fits into `loc`. (Think a really, really big index might not fit into an `int`.) https://stackoverflow.com/questions/1181079/stringsize-type-instead-of-int – Robert Mar 01 '20 at 16:41

score 6 · Answer 2 · answered Mar 16 '09 at 18:03

It's not clear from your example what String you're searching for "bob" in, but here's how to search for a substring in C++ using find.

string str1( "Alpha Beta Gamma Delta" );
string::size_type loc = str1.find( "Omega", 0 );

if( loc != string::npos )
{
   cout << "Found Omega at " << loc << endl;
}
else
{
   cout << "Didn't find Omega" << endl;
}

score 4 · Answer 3 · answered Mar 16 '09 at 18:01

4

You are looking for the std::basic_string<> function template:

size_type find(const basic_string& s, size_type pos = 0) const;

This returns the index or std::string::npos if the string is not found.

answered Mar 16 '09 at 18:01

dirkgently

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score 1 · Answer 4 · answered Mar 16 '09 at 18:01

1

I'm not exactly sure what your example means, but for the stl string class, look into find and rfind

answered Mar 16 '09 at 18:01

Perchik

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How to do std::string indexof in C++ that returns index of matching string?

4 Answers4

Linked