我正在尝试使用 lambda function 找到一个特定的结构成员

Question

I have been given the following struct. I have a vector of tps.

struct tp{
  unsigned int channel;
  unsigned int tstart;
  unsigned int tspan;
  unsigned int adcsum;
  unsigned int adcpeak;
  unsigned int flags;
};

I cannot modify the struct nor add an operator to it. I have a vector(all_candidates) of specific tstarts that i need to look for on the vector of tps.

std::vector< TP> Tps; //these are the input TPs.
std::vector< std::pair<double,double> > all_candidates;//every element is a time-tstart from a TP.

const auto& tmp1 = &(all_candidates.at[0].first);
auto first_tp = std::find_if(candidates.begin(),candidates.end(),[&tmp1](const TP& tp_1){return tp_1.first_time == tmp1 ;});

But when i run this code I get a compiling error, the first one being:

 error: reference to non-static member function must be called
    const auto& tmp1 = all_candidates.at[0].first; 

what is the correct syntax to find the TPs given a start? Thanks

Answer 1

As the error tells you, the line

const auto& tmp1 = &(all_candidates.at[0].first);

is the problem. As Algirdas Preidžius noted, it should be all_candidates.at(0) . Also, the second & is superfluous and is interpreted as an address operator. The line should be:

const auto& tmp1 = all_candidates.at(0).first;

However, since tstart is a simple int , there is no need for references here. You could simple write:

const int tmp1 = all_candidates.at(0).first;

Likewise, you can just capture tmp1 by value instead of by reference in your lambda.