Multiple make

To clean multiple folders at once:

echo base_path/{subfolder1,subfolder2} | xargs -n 1 make clean -C

RPM atomated building

If your are providing sources or binaries of your software as RPMs you should be aware of a smart way of automating RPM creation.
To create RPM building environment:

1. create ~/.rpmmacros with the following content:
   

   
   %_topdir .../rpm #Arbitrary
   %_tmppath /tmp/rpm #Optional 
   

   
   Three dots here denote your favorite RPM building directory infrastructure root. (/home/username will do)
   
2. use the following script:
   

   
   #!/bin/sh
   for d in _topdir _sourcedir _rpmdir _srcrpmdir _specdir _builddir _tmppath; do
     mkdir -p `rpm --eval %{$d}`
   done
   

   
   

In your RPM generation script use constructions like

# Doesn't override previously set value. See Parameter Expansion
SOURCES=${SOURCES:-`rpm --eval %{_sourcedir}`} 
#Assumes your sources are in $PROJECTS/$PROJECT directory
tar --wildcards --exclude \*\.svn\* --exclude \*\~ \ -C "$PROJECTS" -zcf "$SOURCES/$PROJECT.tar.gz" $PROJECT
rpmbuild -ba "$PROJECTS/$PROJECT/$PROJECT.spec"

Following this recommendation you will never need to force your packagers to use a harcoded SOURCES folder or to do configuration of your package with their RPM settings.

Again, thanks to comrade Buzykaev, for his tar command idea

Bash versioning

Here is the bash command:

cp -i aaa/bbb/ccc/ddd/xxxx_{6,7}.tpl

This expands to

cp -i aaa/bbb/ccc/ddd/xxxx_6.tpl aaa/bbb/ccc/ddd/xxxx_7.tpl

This feature of bash is called Brace Expansion and can ease versioning of files based on filesystem. If you have a sequence of files with versions assigned to them as incremented part of the name, you can easily create one more with the given command:

> ls
aaa/bbb/ccc/ddd/xxxx_4.tpl
aaa/bbb/ccc/ddd/xxxx_5.tpl
aaa/bbb/ccc/ddd/xxxx_6.tpl
> cp -i aaa/bbb/ccc/ddd/xxxx_{6,7}.tpl
> ls
aaa/bbb/ccc/ddd/xxxx_4.tpl
aaa/bbb/ccc/ddd/xxxx_5.tpl
aaa/bbb/ccc/ddd/xxxx_6.tpl
aaa/bbb/ccc/ddd/xxxx_7.tpl

Even nicer usage:

cp filename{,_`date '+%F'`}

A floating point and C++ templates

Find a bug in the following line:
double sum = std::accumulate(V.begin(), V.end(), 0);


Think more...


This bug can't be easiliy avoided as the connection between internal accumulator variable, return value and third argument types is not obvious and is very well incapsulated by implementation.

The right answer is:
double sum = std::accumulate(V.begin(), V.end(), double(0)); //0.L gives off the same effect

Here is GNU implementation of template function in question:

  /**
   *  @brief  Accumulate values in a range.
   *
   *  Accumulates the values in the range [first,last) using operator+().  The
   *  initial value is @a init.  The values are processed in order.
   *
   *  @param  first  Start of range.
   *  @param  last  End of range.
   *  @param  init  Starting value to add other values to.
   *  @return  The final sum.
   */
  template
    inline _Tp
    accumulate(_InputIterator __first, _InputIterator __last, _Tp __init)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first)
        __init = __init + *__first;
      return __init;
    }

Empty structures in C and C++

//test.c
#include <stdio.h>

struct Temp0{};
struct Temp1{char a;};

int main() {
    printf("Temp0 size: %d\n", sizeof(struct Temp0));
    printf("Temp1 size: %d\n", sizeof(struct Temp1));
    return 0;
}

This code being compiled with GNU toolchain gives the following results:

$ gcc test.c -o test && ./test
Temp0 size: 0
Temp1 size: 1



$ g++ test.c -o test && ./test
Temp0 size: 1
Temp1 size: 1


The reasons explained

I wonder are other toolchains give the same results...

Gnome-terminal and gconf

Recently there was a usual problem with gnome-terminal in Debian testing. As gconf is updated, gnome-terminal won't start gconf by itself.
Manual update of gnome-terminal (to version 2.26) from unstable release solves the problem.