C/C++

Problem:

You have a hash data structure represented by CZMQ’s zhash_t (see the zhash_t documentation for further information).

In order to be able to use it more conveniently in C++, you intend to convert said zhash_t to a std::map<std::string, std::string>.

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Problem:

You want to use readlink() to get the file or directory a symbolic link points to, but you don’t know the buffer size that is required to store the symlink destination. You don’t want to allocate an incredibly large amount of memory (whatever amount you choose, it could always be insufficient), but you won’t risk buffer overflows.

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Problem:

You’ve got a gzipped file that you want to decompress using C++. You don’t want to use pipes to gzip in an external process. You don’t want to use zlib and manual buffering either.

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Problem:

You want to use mmap() from sys/stat.h POSIX header to map a file for reading (not writing). You can’t find any simple bare example on the internet.

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Problem:

You want to use stat() from sys/stat.h POSIX header in order to get the size of a file.

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Problem:

You want to use the mkdir() function from the sys/stat.h POSIX header, but you don’t know what the mode_t argument should look like.

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The following C++ program uses boost::iostreams to memory-map a file, read it’s content into a std::string and print it to cout.

It provides a minimal example of how to use the boost::iostreams portable mmap functionality.

//Compile like this: g++ -o mmap mmap.cpp -lboost_iostreams
#include <boost/iostreams/device/mapped_file.hpp>
#include <iostream>
#include <string>
using namespace std;
using namespace boost::iostreams;

int main(int argc, char** argv) {
   //Initialize the memory-mapped file
   mapped_file_source file(argv[1]);
   //Read the entire file into a string
   string fileContent(file.data(), file.size());
   //Print the string
   cout << fileContent;
   //Cleanup
   file.close();
}

Also see A simple mmap() readonly example

Problem:

In C++ you want to check if a given file exists, but you can’t use stat() because your code needs to work cross-plaform.

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Problem:

In C++11 you want to iterate over a smart pointer (auto_ptr, shared_ptr, …). collection, say a std::vector, using the new for loop syntax.

Let’s try it out:

using namespace std;
shared_ptr<vector<int> > smartptr(/* A ptr to your vector */);
for(int s : smartptr) {
    /* do something useful */
}

When trying to compile this code, GCC emits the following error message (other lines are omitted for the sake of simplicity)

error: no matching function for call to 'begin(std::shared_ptr<std::vector<int> >&)'
error: no matching function for call to 'end(std::shared_ptr<std::vector<int> >&)'

or, when LANG=de is set:

Fehler: keine passende Funktion für Aufruf von »begin(std::shared_ptr<std::vector<int> >&)«
Fehler: keine passende Funktion für Aufruf von »end(std::shared_ptr<std::vector<int> >&)«

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Problem:

In NodeJS, you got a size of a file in bytes, but you want to format it for better readability.
For example, if your size is 10000 bytes, you want to print 10 kilobytes, but if it is 1200000, you want to print 1.20 Megabytes.

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