Hi marcel, > can someone explain it to me? The *STANDARD* says that pop_back on an empty std::vector has an undefined effect. The safer version you suggest complies with the standard -- but it's not reliable behavior on all C++ compilers, and it has a performance penalty for code that does not expect nor rely upon the safe behavior you've suggested. Even though the performance penalty is slight, it is enough that certain situations may opt not to use std::vector because of the performance overhead. You can get that same safe behavior by doing a if(v.size()) v.pop_back(); in your code. Or better yet, create a marcel::vector template class that adds the additional safety feature you desire *AND* is cross-platform compatible. That same guarantee cannot be made of the std:: namespace's implementation of std::vector. HTH, --Eljay
