The There are three character types: char, signed char, and unsigned char are collectively called the character types. Compilers have the latitude to define char to have the same range, representation, and behavior as either signed char or unsigned char. Irrespective of the choice made, char is a separate type from the other two and is not compatible with either.
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In most cases, the only portable operators on plain char types are assignment and equality operators (=, ==, != ). An exception is the translation to and from digits. For example, if the char c is a digit, c - '0' is a value between 0 and 9.
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The following noncompliant code example simply shows calling the standard string handling function strlen() being called with a plain character string, a signed character string, and an unsigned character string. The strlen() functions takes a single argument of type const char *.
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Compiling at high warning levels in compliance with guideline [MSC00-C. Compile cleanly at high warning levels] causes warnings to be issued when converting from {{unsigned char\[\]}} to {{const char *}} when {{char}} is signed and from {{signed char\[\]}} to {{const char *}} when {{char}} is defined to be unsigned. Casts are required to eliminate these warnings, but excessive casts can make code difficult to read and hide legitimate warning messages. |
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Conversions are not required, and the code compiles cleanly at high warning levels without casts.
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Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
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STR04-C | low | unlikely | low | P3 | L3 |
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Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Other Languages
Related Guidelines
This rule appears in the C++ Secure Coding Standard as : STR04-CPP. Use plain char for characters in the basic character set.
Bibliography
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\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 6.2.5, "Types" \[[MISRA 042004|AA. Bibliography#MISRA 04]\] Rule 6.1, "The plain char type shall be used only for the storage and use of character values" |
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