The C standard specifies specific strings to use for the mode for the function fopen(). An implementation may define extra strings that define additional modes, but only the modes in the following table (adapted from the C99 standard) are fully portable and C99 compliant:
|
Result |
|---|---|
r |
open text file for reading |
w |
truncate to zero length or create text file for writing |
a |
append; open or create text file for writing at end-of-file |
rb |
open binary file for reading |
wb |
truncate to zero length or create binary file for writing |
ab |
append; open or create binary file for writing at end-of-file |
r+ |
open text file for update (reading and writing) |
w+ |
truncate to zero length or create text file for update |
a+ append; |
open or create text file for update, writing at end-of-file |
r+b or rb+ |
open binary file for update (reading and writing) |
w+b or wb+ |
truncate to zero length or create binary file for update |
a+b or ab+ |
append; open or create binary file for update, writing at end-of-file |
Risk Assessment
Using a non-standard mode will lead to undefined behavior, likely causing the call to fopen() to fail.
Rule |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
FI011-A |
1 (low) |
2 (probable) |
3 (low) |
P6 |
L2 |
References
[[ISO/IEC 9899-1999:TC2]] Section 7.9.15.3, "The fopen function"