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The fopen() function does not provide a mechanism to explicitly specify file access permissions. In the example below, if the call to fopen() creates a new file, the access permissions for that file will be implementation defined. Note that on POSIX compliant systems the permissions may be influenced by the value of umask(). More information on umask() is available in the POSIX specification.

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FILE * fptr = fopen(file_name, "w");
if (!fptr){
  /* Handle Error */
}
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Note that on POSIX compliant systems the permissions may be influenced by the value of umask(). More information on umask() is available in the POSIX specification.

Compliant Solution

The fopen_s() function defined in ISO/IEC TR 24731-2006 provides some control over file access permissions. Specifically, the report states: "If the file is being created, and the first character of the mode string is not 'u', to the extent that the underlying system supports it, the file shall have a file permission that prevents other users on the system from accessing the file."

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