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Conoscenza Silente

22 Jul 2010 22 Jul '10

11:36 a.m.

Hi All I created a lambda expression inside my std::for_each call. Inside it there is code like this one, but I have building error telling me that error: expected primary-expression before ‘break’ error: expected `]' before ‘break’ Do you know what it is and how to fix it? The same applies to return statement Thanks AFG namespace bl = boost::lambda; int a, b; bl::var_type< int >::type a_( bl::var( a ) ); bl::var_type< int >::type b_( bl::var( b ) ); std::for_each( v.begin(), v.end(), ( if_( a_ > _b_ ) [ std::cout << _1, break ] ));

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OvermindDL1

22 Jul 22 Jul

11:45 a.m.

On Thu, Jul 22, 2010 at 5:36 AM, Conoscenza Silente wrote:

Hi All I created a lambda expression inside my std::for_each call. Inside it there is code like this one, but I have building error telling me that

error: expected primary-expression before ‘break’ error: expected `]' before ‘break’

Do you know what it is and how to fix it? The same applies to return statement Thanks AFG

namespace bl = boost::lambda; int a, b; bl::var_type< int >::type a_( bl::var( a ) ); bl::var_type< int >::type b_( bl::var( b ) );

std::for_each( v.begin(), v.end(), ( if_( a_ > _b_ ) [ std::cout << _1, break ] ));

'break' is not a lazy command, hence it will not work there. What are you even trying to do anyway?

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Conoscenza Silente

12:06 p.m.

Well I was willing to do 2 things * to use call 'break' to get out of the std::for_each * to use return to exit out of the class function having this code. For the 'break' command now I found other means ( shame on me: I can't use break in a std::for_each like if ..typed without too much thinking ..sorry ) but still I don't know how to fix the call to 'return'. If I put a call to 'return' in lambda expression inside std::for_each to exit the function I have the same error. On Thu, Jul 22, 2010 at 1:45 PM, OvermindDL1 wrote:

On Thu, Jul 22, 2010 at 5:36 AM, Conoscenza Silente wrote:

...
Hi All I created a lambda expression inside my std::for_each call. Inside it there is code like this one, but I have building error telling me that

error: expected primary-expression before ‘break’ error: expected `]' before ‘break’

Do you know what it is and how to fix it? The same applies to return statement Thanks AFG

namespace bl = boost::lambda; int a, b; bl::var_type< int >::type a_( bl::var( a ) ); bl::var_type< int >::type b_( bl::var( b ) );

std::for_each( v.begin(), v.end(), ( if_( a_ > _b_ ) [ std::cout << _1, break ] ));

'break' is not a lazy command, hence it will not work there. What are you even trying to do anyway? _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

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OvermindDL1

11:06 p.m.

On Thu, Jul 22, 2010 at 6:06 AM, Conoscenza Silente wrote:

Well I was willing to do 2 things * to use call 'break' to get out of the std::for_each * to use return to exit out of the class function having this code. For the 'break' command now I found other means ( shame on me: I can't use break in a std::for_each like if ..typed without too much thinking ..sorry ) but still I don't know how to fix the call to 'return'. If I put a call to 'return' in lambda expression inside std::for_each to exit the function I have the same error.

Please do not top post... std::for_each is basically implemented like: template b_ ) [ std::cout << _1, break ] ) Creates a function equivalent to this: template<typename t> void phoenixfunc(t &_1) { if( a_ > b_ ) { std::cout << _1 // place 1 } } Now, you are trying to put a break in "place 1", as you can see, break makes absolutely no sense there. If you try to put a return, only thing it does is just exit the function, which it is doing anyway, so it is useless (and since return is not lazy, it does not work anyway). So again, not quite sure what you are trying to accomplish. If you are trying to bail out of a for_each early, then you are using it incorrectly, a std::for_each is designed to iterate over each element in an iterator, if you want to stop at a point, then perhaps use std::find. If you really must use std::for_each for whatever reason, then you have to throw an exception to exit, and catch it outside of it.

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OvermindDL1

11:07 p.m.

On Thu, Jul 22, 2010 at 5:06 PM, OvermindDL1 wrote:

std::for_each is basically implemented like:

template

Whoops, meant like this: template

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Conoscenza Silente

23 Jul 23 Jul

5:26 a.m.

Hi OvermindDL1 You covered all possible usage of it I need. Thanks for the great response. Kind Regards AFG

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OvermindDL1

6:12 a.m.

On Thu, Jul 22, 2010 at 11:26 PM, Conoscenza Silente wrote:

Hi OvermindDL1 You covered all possible usage of it I need. Thanks for the great response. Kind Regards AFG

No problem, it is always fun working through problems. :)

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