Page History

Do not call a function with the wrong number or type of arguments. 

The C Standard identifies five distinct situations in which undefined behavior (UB) may arise as a result of invoking a function using a declaration that is incompatible with its definition or by supplying incorrect types or numbers of arguments:

An application programming interface (API) specifies how a function is intended to be called. Calling a function with incorrect arguments can result in unexpected or unintended program behavior. Functions that are appropriately declared (as in DCL07DCL40-C. Include the appropriate type information in function declarators) will typically fail compilation Do not create incompatible declarations of the same function or object) will typically generate a compiler diagnostic message if they are supplied with the wrong number or types of arguments. However, there are cases where in which supplying the incorrect arguments to a function will, at best, generate compiler warnings. These Although such warnings should be resolved but , they do not prevent program compilation. (See MSC00-C. Compile cleanly at high warning levels.)

Noncompliant Code Example

...

The header <tgmath.h> provides type-generic macros for math functions. Although most functions from the <math.h> header have a complex counterpart in <complex.h>, several functions do not. Calling any of the following type-generic functions with complex values is undefined behavior.

Functions That Should Not Be Called with Complex Values

atan2()	erf()	fdim()	fmin()	ilogb()	llround()	logb()	nextafter()	rint()	tgamma()
cbrt()	erfc()	floor()	fmod()	ldexp()	log10()	lrint()	nexttoward()	round()	trunc()
ceil()	exp2()	fma()	frexp()	lgamma()	log1p()	lround()	remainder()	scalbn()
copysign()	expm1()	fmax()	hypot()	llrint()	log2()	nearbyint()	remquo()	scalbln()

This noncompliant code example attempts to take the base-2 logarithm of a complex number, resulting in undefined behavior:

Code Block
bgColor #ffcccc lang c
#include <tgmath.h>   void func(void) { double complex c = 2.0 + 4.0 * I; double complex result = log2(c); }

Compliant Solution (Complex Number)

If the clog2() function is not available for an implementation as an extension, the programmer can take the base-2 logarithm of a complex number, using log() instead of log2(), because log() can be used on complex arguments, as shown in this compliant solution:

#include <tgmath.h>
 
void func(void) {
  double complex c = 2.0 + 4.0 * I;
  double complex result = log(c)/log(2);
}

Compliant Solution (Real Number)

The programmer can use this compliant solution if the intent is to take the base-2 logarithm of the real part of the complex number:

#include <tgmath.h>
 
void func(void) {
  double complex c = 2.0 + 4.0 * I;
  double complex result = log2(creal(c));
}

Noncompliant Code Example

In this noncompliant example, the C standard library function strchr() is called through the function pointer fp declared with a prototype with incorrectly typed arguments. According to the C Standard, 6.3.2.3, paragraph 8 [ISO/IEC 9899:2024]

A pointer to a function of one type may be converted to a pointer to a function of another type and back again; the result shall compare equal to the original pointer. If a converted pointer is used to call a function whose type is not compatible with the referenced type, the behavior is undefined.

See undefined behavior 26In this example, the function pointer fp is used to refer to the function strchr(). However, fp is declared without a function prototype. As a result, there is no type checking performed on the call to fp(12,2);.

#include <stdio.h>
#include <string.h>

char *(*fp) ();

int main(void) {
  const char *c;
  fp = strchr;
  c = fp(12'e', 2"Hello");
  printf("%s\n", c);
  return 0;
}

Compliant Solution

...

In this compliant solution, the function pointer fp, which points to the C standard library function strchr(), is declared with the correct parameters and is invoked with the correct number and type of arguments:Declaring fp with a function prototype corrects this example.

Code Block
bgColor #ccccff lang c
#include <stdio.h> #include <string.h> char *(*fp) (const char *, int); int main(void) { const char *c; fp = strchr; c = fp("Hello",'He'); printf("%s\n", c); return 0; }

Noncompliant Code Example

In this noncompliant example, the function f() is defined to take an argument of type long but f() is called from another file with an argument of type int:

/* In another source file */
long f(long x) {
  return x < 0 ? -x : x;
}

/* In this source file, no f prototype in scope */
long f();
 
long g(int x) {
  return f(x);
}

Compliant Solution

In this compliant solution, the prototype for the function f() is included in the source file in the scope of where it is called, and the function f() is correctly called with an argument of type long:

/* In another source file */
 
long f(long x) {
  return x < 0 ? -x : x;
}

/* f prototype in scope in this source file */

long f(long x); 

long g(int x) {
  return f((long)x);  
}

Noncompliant Code Example (

...

POSIX)

The POSIX function open() [Open Group 2004IEEE Std 1003.1:2013] is a variadic function with the following prototype:

...

The open() function accepts a third argument to determine a newly created file's access mode. If open() is used to create a new file , and the third argument is omitted, the file may be created with unintended access permissions. (See FIO06-C. Create files with appropriate access permissions.)

In this noncompliant code example from a vulnerability in the useradd() function of the shadow-utils package CVE-2006-1174, the third argument to open() has been is accidentally omitted.:

fd = open(ms, O_CREAT | O_EXCL | O_WRONLY | O_TRUNC);

Note that technically Technically, it is also incorrect to pass a third argument to open() when not creating a new file (that is, with the O_CREAT flag not set). A POSIX implementation could, if it wished, return an EINVAL error in this case. However, in practice it is unlikely to cause a problem.

Compliant Solution (

...

POSIX)

To correct In this examplecompliant solution, a third argument is specified in the call to open().:

#include <fcntl.h>
 
void func(const char *ms, mode_t perms) {
  /* ... */
  int fd;
  fd = open(ms, O_CREAT | O_EXCL | O_WRONLY | O_TRUNC, file_access_permissionsperms);
  if (fd == -1) {
    /* Handle error */
}
/* ... */}
}

Risk Assessment

Calling a function with incorrect arguments can result in unexpected or unintended program behavior.

Automated Detection

Related Vulnerabilities

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

Related Guidelines

Key here (explains table format and definitions)

...

ISO/IEC 9899:2011 Forward and Section 6.9.1, "Function definitions"

...

...

...

ISO/IEC TR 24772 "OTR Subprogram signature mismatch"

MISRA Rule 16.6

...

...

CERT-CWE Mapping Notes

Key here for mapping notes

CWE-685 and EXP37-C

EXP37-C = Union( CWE-685, CWE-686) Intersection( CWE-685, CWE-686) = Ø

CWE-686 and EXP37-C

Intersection( EXP37-C, FIO47-C) =

• Invalid argument types passed to format I/O function

EXP37-C – FIO47-C =

• Invalid argument types passed to non-format I/O function

FIO47-C – EXP37-C =

• Invalid format string, but correctly matches arguments in number and type

EXP37-C = Union( CWE-685, CWE-686)

Intersection( CWE-685, CWE-686) = Ø

CWE-628 and EXP37-C

CWE-628 = Union( EXP37-C, list) where list =

• Improper ordering of function arguments (that does not violate argument types)

• Wrong argument values or references

Bibliography

...

...

...

Image Modified Image Modified Image Modified