The ISO/IEC 9899-1999 C standard function fopen()
is typically used to open an existing file or create a new one. However, fopen()
does not provide a mechanism to determine if an existing file has been opened or a new file has been created. This may lead to a program overwriting or accessing an unintended file.
In this example, a file name is supplied to fopen()
to create and open for writing. However, there is no guarantee that the file referenced by file_name
does not exist prior to calling fopen()
. This may cause an unintended file to be overwritten.
... FILE * fptr = fopen(file_name, "w"); if (!fptr) { /* Handle Error */ } ... |
The ISO/IEC 9899-1999 C standard does not provide a mechanism to determine if an existing file has been opened or a new file has been created. However, the open()
function as defined by Open Group 04c is available on many platforms and provides such a mechanism. If the O_CREAT
and O_EXCL
flags are used together, the open()
function will fail if the file specified by file_name
already exists.
... int fd = open(file_name, O_CREAT | O_EXCL | O_WRONLY, new_file_mode); if (fd == -1) { /* Handle Error */ } ... |