CODEWITHSUNDEEP
c++filebinarystdvector
Aaron Sear
Aaron Sear

Reputation: 123

how to efficiently read a binary file into a vector C++

I need to read a large binary file (~1GB) into a std::vector<double>. I'm currently using infile.read to copy the whole thing into a char * buffer (shown below) and I currently plan to convert the whole thing into doubles with reinterpret_cast. surely there must be a way to just put the doubles straight into the vector?

I'm also not sure about the format of the binary file, the data was produced in python so it's probably all floats 

ifstream infile(filename, std--ifstream--binary);

infile.seekg(0, infile.end);     //N is the total number of doubles
N = infile.tellg();              
infile.seekg(0, infile.beg);

char * buffer = new char[N];

infile.read(buffer, N);

Upvotes: 10

Views: 13078

Answers (1)

Tony J
Tony J

Reputation: 651

Assuming the entire file is double, otherwise this wont work properly.

std::vector<double> buf(N / sizeof(double));// reserve space for N/8 doubles
infile.read(reinterpret_cast<char*>(buf.data()), buf.size()*sizeof(double)); // or &buf[0] for C++98

Upvotes: 12

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