05. Strings (STR)

Strings are a fundamental concept in software engineering, but they are not a built-in type in C. Null-terminated byte strings consist of a contiguous sequence of characters terminated by and including the first null character. The C programming language supports the following types of null-terminated byte strings: single byte character strings, multibyte character strings, and wide character strings. Single byte and multibyte character strings are both described as null-terminated byte strings.

A pointer to a single byte or multibyte character string points to its initial character. The length of the string is the number of bytes preceding the null character, and the value of the string is the sequence of the values of the contained characters, in order.

A wide string is a contiguous sequence of wide characters terminated by and including the first null wide character. A pointer to a wide string points to its initial (lowest addressed) wide character. The length of a wide string is the number of wide characters preceding the null wide character, and the value of a wide string is the sequence of code values of the contained wide characters, in order.

Null-terminated byte strings are implemented as arrays of characters and are susceptible to the same problems as arrays. As a result, rules and recommendations for arrays should also be applied to null-terminated byte strings.

Recommendations

STR00-A. Use TR 24731 for remediation of existing string manipulation code

STR01-A. Use managed strings for development of new string manipulation code

STR02-A. Sanitize data passed to complex subsystems

Rules

STR30-C. Do not attempt to modify string literals

STR31-C. Do not copy data from an unbounded source to a fixed-length array

STR32-C. Allocated adequate space when copying bounded strings

STR33-C. Guarantee that all strings are null-terminated

STR34-C. Do not truncate strings while copying

STR35-C. Size wide character strings correctly

Risk Assessment Summary

References

• ISO/IEC 9899-1999 Section 7.1.1 Definitions of terms, Section 7.21 String handling <string.h>
• Seacord 05 Chapter 2 Strings