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Abstract data types are not restricted to object-oriented languages like C++ and Java and should be created and used in C language programs , as well. Abstract data types are most effective when used with private (opaque) data types and information hiding.

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struct string_mx {
    size_t size;
    size_t maxsize;
    unsigned char strtype;
    char *cstr;
};

typedef struct string_mx string_mx;

/* Function declarations */
extern errno_t strcpy_m(string_mx *s1, const string_mx *s2);
extern errno_t strcat_m(string_mx *s1, const string_mx *s2);
/* etc. */

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In the external string_m.h file, the string_mx type is defined to be an instance of struct string_mx, which , in turn , is declared as an incomplete type.

struct string_mx;
typedef struct string_mx string_mx;

/* Function declarations */
extern errno_t strcpy_m(string_mx *s1, const string_mx *s2);
extern errno_t strcat_m(string_mx *s1, const string_mx *s2) ;
/* etc. */

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struct string_mx {
    size_t size;
    size_t maxsize;
    unsigned char strtype;
    char *cstr;
};

Modules that implement the abstract data type include both the external and internal definitions, while  whereas users of the data abstraction include only the external string_m.h file. This allows the implementation of the string_mx data type to remain private.

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The use of opaque abstract data types, while  though not essential to secure programming, can significantly reduce the number of defects and vulnerabilities introduced in code, particularly during ongoing maintenance.

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Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

ISO/IEC 9899:19992011 Section 6.2.5, "Types"

Bibliography

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