How to fix “Cannot find crt1.o” on Ubuntu


You’re trying to compile something (e.g. using GCC) on Ubuntu, but you get an error message similar to this one:

/usr/bin/ld: error: cannot open crt1.o: No such file or directory
/usr/bin/ld: error: cannot open crti.o: No such file or directory
/usr/bin/ld: error: cannot open crtn.o: No such file or directory

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Posted by Uli Köhler in Build systems, Linux

How to compile & install libc++ on Linux


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):
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):

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Posted by Uli Köhler in Build systems, C/C++, Linux

git svn: Clone latest revision only


You want to use git-svn to clone a SVN repository, but you don’t want to clone the entire history (which can be quite slow) but only the latest revision.

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Posted by Uli Köhler in git, Shell, Subversion, Version management

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:

  1. Use the g++ LLVM backend
  2. 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.

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Posted by Uli Köhler in C/C++, Databases, LLVM

Efficiently encoding variable-length integers in C/C++

Using fixed width integers is space-inefficient in many cases, especially if the majority of values are low and only use the less-significant bytes.

This guide describes the basics of varint (varying-length integer) encoding while focusing on C++ as programming language, but the basic concepts apply to any language.

Varint encodings use only the bytes that are needed to represent you integer value appropriately. A varint algorithm can represent the number 10 in only one byte while using 4 bytes to encode 800000000 (800 million). In many application this yields a significant overhead reduction since you would need to use larger integers if there is a slight change that your values grow beyond the boundary of the integer type that is applicable for the majority of your values. Additionally, you usually can only use 8,16,32 or 64 bit integers while 48 bit integers need to be coded manually in most languages. For example, if most of your values are between 0 and 100, but a few might be larger than 16384 (for unsigned integers), you would usually use a full 32-bit integer, even if most values could be represented by a single byte.

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Posted by Uli Köhler in Allgemein

Move Minimize, Maximize and Close to the right in Ubuntu Unity

In more recent Ubuntu Versions, the minimize, maximize and close icons have moved to the left upper corner of the window.

If you want them to show up on the right side instead, follow this guide:

  1. Open a terminal (e.g. click on Ubuntu Dashboard and type Terminal, then click on Terminal)
  2. Copy and paste this text into the terminal (Ctrl+V doesn’t work here, use right-click -> insert)
    gconftool-2 -s /apps/metacity/general/button_layout —type=string “menu:minimize,maximize,close”
  3. Press Return / Enter
  4. The icons should shift to the right immediately
Posted by Uli Köhler in Allgemein