Read file-contents into a string in C++ [duplicate]

Question

Possible Duplicate:
What is the best way to slurp a file into a std::string in c++?

In scripting languages like Perl, it is possible to read a file into a variable in one shot.

    open(FILEHANDLE,$file);     $content=<FILEHANDLE>; 

What would be the most efficient way to do this in C++?

Answer 1

Like this:

#include <fstream> #include <string>  int main(int argc, char** argv) {    std::ifstream ifs("myfile.txt");   std::string content( (std::istreambuf_iterator<char>(ifs) ),                        (std::istreambuf_iterator<char>()    ) );    return 0; } 

The statement

  std::string content( (std::istreambuf_iterator<char>(ifs) ),                        (std::istreambuf_iterator<char>()    ) ); 

can be split into

std::string content; content.assign( (std::istreambuf_iterator<char>(ifs) ),                 (std::istreambuf_iterator<char>()    ) ); 

which is useful if you want to just overwrite the value of an existing std::string variable.

Answer 2

The most efficient, but not the C++ way would be:

   FILE* f = fopen(filename, "r");     // Determine file size    fseek(f, 0, SEEK_END);    size_t size = ftell(f);     char* where = new char[size];     rewind(f);    fread(where, sizeof(char), size, f);     delete[] where; 

#EDIT - 2

Just tested the std::filebuf variant also. Looks like it can be called the best C++ approach, even though it's not quite a C++ approach, but more a wrapper. Anyway, here is the chunk of code that works almost as fast as plain C does.

   std::ifstream file(filename, std::ios::binary);    std::streambuf* raw_buffer = file.rdbuf();     char* block = new char[size];    raw_buffer->sgetn(block, size);    delete[] block; 

I've done a quick benchmark here and the results are following. Test was done on reading a 65536K binary file with appropriate (std::ios:binary and rb) modes.

[==========] Running 3 tests from 1 test case. [----------] Global test environment set-up. [----------] 4 tests from IO [ RUN      ] IO.C_Kotti [       OK ] IO.C_Kotti (78 ms) [ RUN      ] IO.CPP_Nikko [       OK ] IO.CPP_Nikko (106 ms) [ RUN      ] IO.CPP_Beckmann [       OK ] IO.CPP_Beckmann (1891 ms) [ RUN      ] IO.CPP_Neil [       OK ] IO.CPP_Neil (234 ms) [----------] 4 tests from IO (2309 ms total)  [----------] Global test environment tear-down [==========] 4 tests from 1 test case ran. (2309 ms total) [  PASSED  ] 4 tests.