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If implemented, this reduces the space for unique names and increases the predictability of the resulting names.  But in general, TR 24731-1 does not establish any criteria for predictability of names.

TR 24731-1 also notes that

After a program obtains a file name using the tmpnam_s function and before the program creates a file with that name, the possibility exists that someone else may create a file with that same name. To avoid this race condition, the tmpfile_s function should be used instead of tmpnam_s when possible. One situation that requires the use of the tmpnam_s function is when the program needs to create a temporary directory rather than a temporary file.

/* ... */
FILE *file_ptr;
char filename[L_tmpnam_s];

if (tmpnam_s(filename, L_tmpnam_s) != 0) {
  /* Handle Error */
}

if (!fopen_s(&file_ptr, filename, "wb+

/* ... */
FILE *file_ptr;
char filename[L_tmpnam_s];

if (tmpnam_s(filename, L_tmpnam_s) != 0) {
  /* Handle Error */
}

if (!fopen_s(&file_ptr, filename, "wb+")) {
  /* Handle Error */
}
/* ... */

...

The file is opened for update with "wb+" mode, which means "truncate to zero length or create binary file for update." To the extent that the underlying system supports the concepts, the file is opened with exclusive (non-shared) access and has a file permission that prevents other users on the system from accessing the file.

It should be possible to open at least TMP_MAX_S temporary files during the lifetime of the program (this limit may be shared with tmpnam_s()). The value of the macro TMP_MAX_S is only required to be 25 by ISO/IEC TR 24731-1.

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access and has a file permission that prevents other users on the system from accessing the file.

It should be possible to open at least TMP_MAX_S temporary files during the lifetime of the program (this limit may be shared with tmpnam_s()). The value of the macro TMP_MAX_S is only required to be 25 by ISO/IEC TR 24731-1.

The tmpfile_s() function is available on systems that support ISO/IEC TR 24731-1.

TR 24731-1 notes the following regarding the use of tmpfile_s instead of }}{{{}tmpnam_s:

After a program obtains a file name using the tmpnam_sfunction and before the program creates a file with that name, the possibility exists that someone else may create a file with that same name. To avoid this race condition, the tmpfile_s function should be used instead of tmpnam_s when possible. One situation that requires the use of the tmpnam_s function is when the program needs to create a temporary directory rather than a temporary file.

/* ... */
if (tmpfile_s(&file_ptr)) {
  /* Handle Error */
}
/* ... */

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