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 way to test file existence potentially allowing a program to overwrite or access and 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.
Non-Compliant Example 1
In this example, a file name is supplied to fopen() to create and open for writing. However, there is no guaruntee that the file referenced by file_name does not exist prior to calling fopen(). This may cause an unintended file to be overwritten.
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...
FILE * fptr = fopen(file_name, "w");
if (!fptr) {
/* Handle Error */
}
...
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Compliant Solution 1.
The open() function (Open Group 04c) provides a a way to test for file existence. 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.
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int fd = open(file_name, O_CREAT | O_EXCL | O_WRONLY, new_file_mode);
if (fd == -1) {
/* Handle Error */
}
...
|
References
- Seacord 05 Chapter 7, File I/O
- ISO/IEC 9899-1999 Sections 7.19.3, Files
- ISO/IEC 9899-1999 Sections 7.19.4, Operations on Files
- Open Group 0c The open function