(C++) Write and read a std::vector to/from a std::stream: example 1

 

This write and read a std::vector to/from a std::stream example demonstrates a basic, yet not a foolproof way. The program its setup is fine: a std::vector is created, written to file, a new std::vector is written from that same file and the program tests if the two std::vectors are identical.

 

The assumptions for this approach to work are:

• Text may not be '<\>'
• Text must not contain any whitespace type

 

Note that the program will issue a failed assert when one of these assumptions are violated.

 

• Download the Qt Creator project 'CppVectorToStreamExample1' (zip)

 

See Write and read a std::vector to/from a std::stream: example 2 for a more elaborated version.

 

 

 

 

 

Technical facts

 

Application type(s)

• Desktop application

Operating system(s) or programming environment(s)

• Lubuntu 12.10 (quantal)

IDE(s):

• Qt Creator 2.5.2

Project type:

• Console application

C++ standard:

• C++11

Compiler(s):

• G++ 4.7.2

Libraries used:

• STL: GNU ISO C++ Library, version 4.7.2

 

 

 

 

 

Qt project file: CppVectorToStreamExample1.pro

 

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QT       -= core gui QMAKE_CXXFLAGS += -std=c++11 -Werror TARGET = CppVectorToStreamExample1 CONFIG   += console SOURCES += main.cpp

 

 

 

 

 

main.cpp

 

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#include <iostream> #include <iterator> #include <cassert> #include <algorithm> #include <fstream> #include <string> #include <vector> std::ostream& operator<<(std::ostream& os, const std::vector<std::string>& v) {   //Check data   #ifndef NDEBUG   std::for_each(v.begin(),v.end(),     [&os](const std::string& s)     {       assert(s != "</>" && "Text must not be '</>'");       assert(std::count(s.begin(),s.end(),' ') == 0 && "Text must not contain spaces");     }   );   #endif   //Write start tag   os << "<>\n";   //Write data   std::for_each(v.begin(),v.end(),     [&os](const std::string& s)     {       os << s << '\n';     }   );   //Write end tag   os << "</>";   return os; } std::istream& operator>>(std::istream& is, std::vector<std::string>& v) {   //Read start tag   {     std::string s; is >> s; assert(s == std::string("<>"));   }   //Read data until end tag   while (1)   {     std::string s;     is >> s;     if (s == std::string("</>")) return is;     v.push_back(s);   } } int main() {   const std::vector<std::string> v(     {       "aahs",       "aals",       "abac",       "abas",       "abba",       "abbe",       "abbs",       "abed",       "abet",       "abid"     }   );   const std::string filename = "tmp.txt";   //Write to file   {     std::ofstream f(filename.c_str());     f << v;   }   //Read from file   {     std::vector<std::string> w;     std::ifstream f(filename.c_str());     f >> w;     if (v != w)     {       std::copy(w.begin(),w.end(),std::ostream_iterator<std::string>(std::cout,"\n"));     }     assert(v == w);   } }