Functions should always be declared with the appropriate function prototype. Failure to specify function prototypes results in If a function being implicitly defined. Without a function prototypeprototype is not available, the compiler will assume the the correct cannot perform checks on the number and type of parameters have been supplied to a function. This can result in unintended and undefined behavior. Wiki Markup
Non-Compliant Code Example
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Non-Compliant Code Example
Failure to specify function prototypes results in a function being implicitly defined. Without a function prototype, the compiler assumes the the correct number and type of parameters have been supplied to a function. This can result in unintended and undefined behavior.
In this non-compliant code example, the definition of func() expects three parameters but is supplied only two. However, because there is no prototype for func(), the compiler assumes that the correct number of arguments has been supplied, and uses the next value on the program stack as the missing third argument.
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func(1, 2);
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int func(int one, int two, int three){
printf("%d %d %d", one, two, three);
return 1;
}
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C99 eliminated implicit function declarations from the C language \[[ISO/IEC 9899-1999:TC2|AA. C References#ISO/IEC 9899-1999TC2]\]. However, many compilers allow compilation of programs containing implicitly defined functions, although they may issue a warning message. These warnings should be resolved \[[MSC00-A|MSC00-A. Compile cleanly at high warning levels]\], but do not prevent program compilation. |
Compliant Solution
To correct this example, the appropriate function prototype for func() should be specified.
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