Mode Strings for fopen()

Introduction

Mode String	Meaning
"r"	Open a text file for reading.
"w"	Open a text file for writing, truncating an existing file to zero length, or creating the file if it does not exist.
"a"	Open a text file for writing, appending to the end of an existing file, or creating the file if it does not exist.
"r+"	Open a text file for both reading and writing.
"w+"	Open a text file for reading and writing, first truncating the file to zero length if it exists or creating the file if it does not exist.
"a+"	Open a text file for reading and writing, appending to the end of an existing file, or creating the file if it does not yet exist; the whole file can be read, but writing can only be appended.
"rb" , "wb" , "ab" , "ab+" , "a+b" , "wb+" , "w+b", "ab+" , "a+b"	For binary file
"wx" , "wbx" , "w+x" , "wb+x" or "w+bx"	Like the non-x modes, except they fail if the file already exists and they open a file in exclusive mode, if possible.