How would one push back an empty vector of pairs to another vector?

Question

``` std::vector > > offset_table; for (int i = 0; i < (offset.Width()*offset.Width()); ++i) { offset_table.push_back( std::vector< std::pair > ); } ``` This is my code, but I am getting the errors: ``` main.cpp: In function ‘void Compress(const Image&, Image&, Image&, Image&)’: main.cpp:48:66: error: expected primary-expression before ‘)’ token ``` I do not want any values in the pairs, I just would like to have a vector of empty vectors at the moment. How would I do this?

Accepted Answer

You want to construct a vector to pass to push_back and you're just missing parentheses: ``` offset_table.push_back( std::vector< std::pair >() ); ``` Or, instead of your loop, you could just do the following. It's better because the vector will allocate just the right amount of memory in a single allocation: ``` offset_table.resize( offset.Width()*offset.Width(), std::vector< std::pair >() ); ``` Or this, which is more concise because it's using resize's default 2nd argument: ``` offset_table.resize( offset.Width()*offset.Width() ); ```

How would one push back an empty vector of pairs to another vector?

Solution

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