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.
03
Nov
2013
C/C++
02
Nov
2013
Reading QUASAR scoring matrices in C++
Problem:
You want to read alignment matrices like BLOSUM62 in the QUASAR format. The solution needs to be integrable into C++ code easily.
21
Aug
2013
A simple mmap() readonly example
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.
21
Aug
2013
How to get filesize using stat() in C/C++
Problem:
You want to use stat() from sys/stat.h POSIX header in order to get the size of a file.
05
Apr
2013
How to use mkdir() from sys/stat.h
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.
31
Mar
2013
mmap with Boost IOStreams: A minimalist’s example
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
29
Mar
2013
Reading TAR files in C++
This article describes a method of reading TAR archives (including .tar.gz and .tar.bz2) in C++ using Boost IOStreams.
You could use libtar for this, but the original version hasn’t been updated since 2003 and doesn’t provide you flexibility and insight to the internal structure of a TAR archive. Continue reading →
15
Mar
2013
Simple C++ HTTP download using libcurl easy API
Problem
Using the libcurl easy API you want to download a file using HTTP GET. No extended features such as authentication shall be used.
The download result shall be stored in a std::string
17
Feb
2013
How to compile & install libc++ on Linux
Problem:
You want to compile and install libc++ (sometimes also named libcxx), but CMake complains with this error message
CMake Error at cmake/Modules/MacroEnsureOutOfSourceBuild.cmake:7 (message):
libcxx requires an out of source build. Please create a separate</em>
build directory and run 'cmake /path/to/libcxx [options]' there.
Call Stack (most recent call first):
CMakeLists.txt:24 (MACRO_ENSURE_OUT_OF_SOURCE_BUILD)
CMake Error at cmake/Modules/MacroEnsureOutOfSourceBuild.cmake:8 (message):
In-source builds are not allowed.
CMake would overwrite the makefiles distributed with Compiler-RT.
Please create a directory and run cmake from there, passing the path
to this source directory as the last argument.
This process created the file `CMakeCache.txt' and the directory `CMakeFiles'.
Please delete them.
Call Stack (most recent call first):
CMakeLists.txt:24 (MACRO_ENSURE_OUT_OF_SOURCE_BUILD)
09
Feb
2013
Compiling LevelDB as LLVM binary on Linux
Some time ago I wrote a guide on how to compile and install LevelDB on Linux.
Recently I’m desperately trying to get into LLVM and a tutorial series on how to use LLVM with C/C++ is coming shortly.
As I’m using LevelDB in many of my projects I’d like a way of generating a LLVM IR (intermediate representation) of the LevelDB C++ source – I could link a LLVM program to the native binary, but in order to profit from LLVMs features I suppose using IRs for as many dependencies as possible is the way to go.
Generally there are two ways to go:
- Use the g++ LLVM backend
- Use clang++
I usually tend to use clang++ for LLVM tasks because even with colorgcc and some recent improvements in gcc error message generation I prefer the clang++ error messages, even if I have way more experience with gcc error messages. Additionally the g++ with LLVM backend does seem to have some bugs, including interpreting -emit-llvm as -e -m -i …, plus recent distribution versions don’t work too well with the LLVM gold plugin and it has proved difficult to tell GCC reliably that it shall use llvm-ld as linker.
03
Feb
2013
How to resolve the GCC error message “default argument for parameter of type … has type …”
Problem:
You encounter a GCC error message of the form
error: default argument for parameter of type <some type> has type <some other type>
11
Jan
2013
C++: Check if file exists
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.
02
Jan
2013
A text-to-Brainfuck/RNA converter in ANSI C99
Brainfuck encoder
The following small ANSI C99 program reads a String from stdin and prints out a Brainfuck program that prints the same String on stdout.
Compile using gcc -o bf bf.c
Use it like this:
cat my.txt | ./bf > my.bf
Source code:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char** argv) {
unsigned char c;
unsigned char curval = 0;
//Initialize reg+1 with 8
while(1) {
c = getchar();
if(feof(stdin)) {break;}
while(curval != c) {
if(curval < c) {
putchar('+');
curval++;
} else if(curval > c) {
putchar('-');
curval--;
}
}
putchar('.');
}
}How does it work?
Basically it uses just one of the registers of the Brainfuck Turing machine and incremets or decrements the register to be able to print out the next byte. It doesn’t use any of the more ‘advanced’ features in Brainfuck like loops.
20
Nov
2012
C/C++ Base64 codec using libtomcrypt
Problem:
In C/C++ you want to encode/decode something from/to Base64. libtomcrypt is WTFPL-licensed and therefore provides a good choice for both commercial and non-commercial projects.
19
Nov
2012
Calculating cryptographic hashes using libtomcrypt in C/C++
Problem:
You want to calculate a hash of any string in C/C++. LibTomCrypt is WTFPL licensed, so it’s a good choice for commercial and non-commercial projects.
17
Sep
2012
C++11 : Iterate over smart pointers using foreach loop
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> >&)«
16
Sep
2012
Automatically format size string in Node.js
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.