c++ - Reading data from a file and storing each line in an array? -

i have file lines of integers. want read each line slot in array. have code below, not work. i'm not sure if i'm on right track.

void read_save() {     ifstream in;     int arr[100];     string line;     in.open("file.txt");     while (in.peek() != eof)     {         getline(in, line, '\n');         strcpy(arr, line.c_str());     }     in.clear(); in.close(); } 

there several ways parse integer value out of string.

first, let's fix loop:

int pos = 0; while( std::getline(in, line) && pos < 100 ) {     int value = 0;      // insert chosen parsing method here      arr[pos++] = value; } 

here non-exhaustive list of common options:

1. use std::strtol

   // return 0 on error (indistinguishable parsing actual 0) value = std::strtol( line.c_str(), nullptr, 10  ); 

2. use std::stoi

   // throw exception on error value = std::stoi( line ); 

3. build std::istringstream , read it:

   std::istringstream iss( line ); iss >> value; if( !iss ) {     // failed parse value. } 

4. use std::sscanf

   if( 1 != std::sscanf( line.c_str(), "%d", &value ) ) {     // failed parse value. } 

now, note bounds-test on loop checking pos < 100. because array has storage limit. actually, have overridden global 1 local 1 in read_save, hiding smaller array lost when function finishes.

you can have arbitrary-sized "array" (not array) using other container types provided standard library. useful ones provide random access std::vector , std::deque. let's use vector , change definition of read_save bit more useful:

std::vector<int> read_save( std::istream & in ) {     std::vector<int> values;     std::string line;      for( int line_number = 1; getline( in, line ); line_number++ )     {         try {             int value = std::stoi( line );             values.push_back( value );         }         catch( std::bad_alloc & e )         {             std::cerr << "error (line " << line_number << "): out of memory!" << std::endl;             throw e;         }         catch( std::exception & e)         {             std::cerr << "error (line " << line_number << "): " << e.what() << std::endl;         }     }      return values; } 

and finally, call becomes:

std::ifstream in( "file.txt" ); std::vector<int> values = read_save( in );