remove element from vector<string>

**waxydock** · 06-30-2005

hi,

im trying to remove all elements starting with the a...im not sure why this doesnt work?

Code:

/* remove element if it begins with a */
	for (vector<string>::iterator k = final.begin(); k!=final.end(); ++k) {
		if(*k.find("a")==0)
			final.erase(*k);
	}

thanks..

**Daved** · 06-30-2005

The call to erase invalidates the iterator k. You must use the return value from erase to get the next available iterator. You should also pass the iterator to erase, not the string.

Code:

	for (vector<string>::iterator k = final.begin(); k!=final.end(); ) {
		if(*k.find("a")==0)
			k = final.erase(k);
		else
			++k;
	}

**waxydock** · 06-30-2005

hmmm..still doesnt compile....error msg below

test.cpp: In function `std::vector<std::string, std::allocator<std::string> >
readFruit()':
test.cpp:50: error: `find' undeclared (first use this function)
test.cpp:50: error: (Each undeclared identifier is reported only once for each
function it appears in.)
test.cpp:51: error: no matching function for call to `std::vector<std::string,
std::allocator<std::string> >::erase(std::basic_string<char,
std::char_traits<char>, std::allocator<char> >&)'

**xErath** · 06-30-2005

noob error

Code:

*k.find("a")
k->find("a")

http://www.cppreference.com/operator_precedence.html

to remove the string from the vector do

Code:

for(vector<string>::iterator k = ... ; ... ; ...) //bla bla bla
    if(k->find("whatever") == 0)
        thy_vector.erase(k);

yes, it receives the pointer, not the dereferenced string

**Daved** · 06-30-2005

Instead of using find, you should just check to see if the string is not empty and the first character is 'a' (e.g. if (!k->empty() && k[0] == 'a')).

**waxydock** · 06-30-2005

Thank you xErath...yes im a nubie!

**xErath** · 06-30-2005

ups.. me errors sometime

Code:

for(vector<string>::iterator k = ... ; ... ; ...) //bla bla bla
    if(k->find("whatever") == 0)
        thy_vector.erase(k--);

k-- to revisit the new string in the next cicle, which is pushed backwards by erase

**Daved** · 06-30-2005

What if k is equal to begin()? The method I posted above is probably better for this case.

**hk_mp5kpdw** · 07-01-2005

Use the remove_if function in <algorithm> along with the vector's erase member function:

Code:

bool StartsWitha(const std::string& str)
{
    // Return true for any string beginning with lower-case 'a'
    return str.length() && str[0] == 'a';
}

...

// Erase all strings beginning with 'a' from the vector
final.erase( std::remove_if( final.begin(), final.end(), StartsWitha ), final.end() );

**CornedBee** · 07-01-2005

It's faster if you make that a functor instead of a function.

Code:

struct starts_with_a {
  bool operator ()(const std::string &str) {
    return !str.empty() && str[0] == 'a';
  }
};

final.erase( std::remove_if( final.begin(), final.end(), starts_with_a() ), final.end() );

This way, the compiler can inline the call.

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