Reviewing code doesn't necessarily require actually building it, but it's often helpful to do so in order to evaluate fully. I usually create a CMake project and build from there. Since we're all about code here, naturally, I decided to automate part of the process. Specifically, here's how to use this code:

  1. Hit "edit" on the question of interest that contains one or more C or C++ source code files
  2. Select the entire editable question and paste into a local text file with some appropriate name (this one might be autoproject.md)
  3. run this code using the command line autoproject project.md

Update: I've just created a Python .md file fetcher that replaces the first two steps above.

Note: This code and its companion Python project are now available in a github repo.

This will automatically parse the project.md file and extract the files it finds to a directory tree like this.

├── build                   (empty subdirectory)
├── CMakeLists.txt          (generated)
└── src
    ├── CMakeLists.txt      (generated)
    ├── project.cpp         (extracted)
    ├── test.cpp            (extracted)
    └── project.h           (extracted)

For much code in many questions, all that is then required is to navigate to the build directory and then type:

cmake ..

The executable (if successfully created) will be created in build/src and will be named project (or whatever more meaningful name you have given the original .md file). Examples of questions for which this works are Recursive Breadth First Search for Knights Tour and Hangman on the C++ommand line.

Note that this will not work if there are special things needed by the code in question. For instance, this code itself will not build unless this line is added to the src/CMakeLists.txt file (assuming g++):

target_link_libraries(${EXECUTABLE_NAME} stdc++fs)

The reason is that it uses the C++17 filesystem feature which is still in the experimental namespace and so must, for now must be linked with libstdc++fs. Note also, that CMake will automatically use the environment variables CFLAGS and CXXFLAGS. My setup, which works well for many programs including this one includes CXXFLAGS="-Wall -Wextra -pedantic -std=c++14". The important part here is that this particular program should be compiled with C++14 compatibility. I have not yet tried this code on platforms other than Linux.

I'm interested in a general code review, and particularly if there are improvements that could or should be made to the design or interface to the AutoProject class.

Here are the files:


#include <string>
#include <fstream>
#include <vector>
#include <exception>
#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;

class FileExtensionException : public std::runtime_error
    FileExtensionException(const std::string& msg) :

class AutoProject {
    AutoProject() = default;
    AutoProject(fs::path mdFilename);
    void open(fs::path mdFilename);

    bool createProject();
    void writeTopLevel() const;
    void writeSrcLevel() const;
    void copyFile() const;
    const std::vector<fs::path>&filenames() const {
        return srcnames;

    static const std::string mdextension;  
    bool isIndented(const std::string& line) const;
    void emit(std::ostream& out, const std::string &line) const;
    std::string trimExtras(std::string& line) const;
    bool isSourceFilename(std::string& line) const;

    static std::string& trim(std::string& str, char ch);
    static std::string& rtrim(std::string& str, char ch);
    static constexpr unsigned indentLevel{4};
    fs::path mdfile;
    std::string projname;
    std::string srcdir;
    std::ifstream in;
    std::vector<fs::path> srcnames;


#include "AutoProject.h"
#include <unordered_set>
#include <algorithm>
#include <iostream>

const std::string AutoProject::mdextension{".md"};  

void AutoProject::open(fs::path mdFilename)  {
    AutoProject ap(mdFilename);
    std::swap(ap, *this);

AutoProject::AutoProject(fs::path mdFilename) : 
    srcdir{projname + "/src/"},
    if (mdfile.extension() != mdextension) {
        throw FileExtensionException("Input file must have " + mdextension + " extension");
    if (!in) {
        throw std::runtime_error(std::string("Cannot open input file ") + mdfile.c_str());
    if (fs::exists(srcdir)) {
        throw std::runtime_error(projname + " already exists: will not overwrite.");
    if (!fs::create_directories(srcdir)) {
        throw std::runtime_error(std::string("Cannot create directory ") + srcdir);
    fs::create_directories(projname + "/build/");

/// returns true if passed file extension is an identified source code extension.
bool isSourceExtension(const std::string &ext) {
    static const std::unordered_set<std::string> source_extensions{".cpp", ".c", ".h", ".hpp"};
    return source_extensions.find(ext) != source_extensions.end();

void AutoProject::copyFile() const {
    // copy md file to projname/src
    fs::copy_file(mdfile, srcdir + projname + mdextension);

bool AutoProject::createProject() {
    std::string prevline;
    bool infile = false;
    std::ofstream srcfile;
    fs::path srcfilename;
    for (std::string line; getline(in, line); ) {
        // scan through looking for lines indented with indentLevel spaces
        if (infile) {
            // stop writing if non-indented line or EOF
            if (!line.empty() && !isspace(line[0])) {
                prevline = line;
                infile = false;
            } else {
                emit(srcfile, line);
        } else {
            if (isIndented(line)) {
                // if previous line was filename, open that file and start writing
                if (isSourceFilename(prevline)) {
                    srcfilename = fs::path(srcdir + prevline);
                    if (srcfile) {
                        emit(srcfile, line);
                        infile = true;
            } else {
                prevline = line;
    return !srcnames.empty();

std::string& AutoProject::trim(std::string& str, char ch) {
    auto it = str.begin();
    for ( ; (*it == ch || isspace(*it)) && it != str.end(); ++it) 
    { }
    if (it != str.end()) {
        str.erase(str.begin(), it);
    return str;

std::string& AutoProject::rtrim(std::string& str, char ch) {
    std::reverse(str.begin(), str.end());
    trim(str, ch);
    std::reverse(str.begin(), str.end());
    return str;

bool AutoProject::isSourceFilename(std::string& line) const {
    return isSourceExtension(fs::path(line).extension());

std::string AutoProject::trimExtras(std::string& line) const
    if (line.empty()) {
        return line;
    // remove header markup
    trim(line, '#');
    // remove bold or italic
    trim(line, '*');
    rtrim(line, '*');
    // remove trailing - or :
    rtrim(line, '-');
    rtrim(line, ':');
    return line;

void AutoProject::writeSrcLevel() const {
    // write CMakeLists.txt with filenames to projname/src
    std::ofstream srccmake(srcdir + "CMakeLists.txt");
    srccmake <<
            "cmake_minimum_required(VERSION 2.8)\n"
            "set(EXECUTABLE_NAME \"" << projname << "\")\n"
    for (const auto& fn : srcnames) {
        srccmake << ' ' << fn;
    srccmake << ")\n";

void AutoProject::writeTopLevel() const {
    // write CMakeLists.txt top level to projname
    std::ofstream topcmake(projname + "/CMakeLists.txt");
    topcmake << 
            "cmake_minimum_required(VERSION 2.8)\n"
            "project(" << projname << ")\n"

bool AutoProject::isIndented(const std::string& line) const {
    size_t indent = line.find_first_not_of(' ');
    if (indent >= indentLevel && indent != std::string::npos) {
        return true;
    return !(indent == 0);

void AutoProject::emit(std::ostream& out, const std::string &line) const {
    if (line.size() < indentLevel) {
        out << line << '\n';
    } else {
        out << (line[0] == ' ' ? line.substr(indentLevel) : line.substr(1)) << '\n';


#include <iostream>
#include "AutoProject.h"

int main(int argc, char *argv[])
    if (argc != 2) {
        std::cerr << "Usage: autoproject project.md\nCreates a CMake build tree under 'project' subdirectory\n";
        return 0;
    AutoProject ap;
    try {
    catch(std::exception& e) {
        std::cerr << "Error: " << e.what() << '\n';
        return 1;
    if (ap.createProject()) {
        std::cout << "Successfully extracted the following source files:\n";
        for (const auto& file : ap.filenames()) {
            std::cout << file << '\n';
  • 3
    \$\begingroup\$ Love this idea. We (as a community) need to take it a step further and pass in the URL of the question rather than having a manual copy and paste step. \$\endgroup\$ Mar 31, 2016 at 16:27
  • 3
    \$\begingroup\$ @LokiAstari Even better, a web service and an auto-generated link on the question. Click -> compile! \$\endgroup\$
    – Emily L.
    Apr 1, 2016 at 15:16
  • 1
    \$\begingroup\$ @EmilyL. Sounds fun. But that means Javascript programming. Which though I do now and again is not my strongest language. While command line means C++ which flys out :-) \$\endgroup\$ Apr 1, 2016 at 15:38
  • \$\begingroup\$ @EmilyL. See codereview.stackexchange.com/questions/124479/… which is a new question describing a Python md file fetcher for use with this program. \$\endgroup\$
    – Edward
    Apr 1, 2016 at 16:51
  • 2
    \$\begingroup\$ I think you should put this and the file fetcher on GitHub, with accompanying build script. Lots of reviewers could make use of this project and I'm interested in adding some features myself. Great work :) \$\endgroup\$
    – jacwah
    Apr 4, 2016 at 19:16

1 Answer 1

for (std::string line; getline(in, line); ) {

This for loop looks weird.

It looks weird because it's a while loop where you've taken advantage of the ability to declare a variable.

I think it'd be better as a while loop:

std::string line;
while(getline(in, line)) {

It's longer, but doesn't make me go "wait, what?" anymore.

// stop writing if non-indented line or EOF
if (!line.empty() && !isspace(line[0])) {

Somewhere else you use isIndented(line). Here your comment says "if non-indented line". Why are you not using your own utility function?

  • 2
    \$\begingroup\$ I generally prefer the reduced scope of the for loop, but it could, of course, be written as while. For the isIndented issue, it's a little tricky. It turns out that the code formatter used here uses different criteria to determine the start and the end of a code block. That difference is why I don't use a single function for both purposes. \$\endgroup\$
    – Edward
    Apr 11, 2016 at 22:10
  • 1
    \$\begingroup\$ c++17 allows while(std::string line; getline(in, line))which is less hackish than the for version, but which looks even more strange (as new syntax). \$\endgroup\$
    – Jarod42
    Jun 27, 2018 at 17:35

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