The answer is YES. A published patent application will act as a defensive disclosure (prior art) to any future patent application(s).
A patent application gets published after 18 months from the date of filing (or priority date, whichever is earlier), unless an early publication is requested.
The patent application is published even if the patent is not granted. However, some countries (ex: US) provide the option of withholding publication even beyond 18 months, if a foreign application is not filed.
For a subject matter to be patentable, it should satisfy 5 criteria namely:
- Patentable subject matter
- Novelty
- Non-obviousness/inventive-step
- Industrial application
- Enablement
The publication of your application will have an impact on the novelty and inventive step requirements of patentability with respect to future applications.
You may want to refer the article at the below link to get insight on strategy one could adopt based on the requirement.
http://www.invntree.com/blogs/are-patents-always-best-way-protect-inventions
For more information about patentability refer:
http://www.invntree.com/blogs/how-can-i-find-out-whether-my-invention-patentable