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By the way, one thing that came up for me last week was that we probably ought to mention conformant array parameters. For example,

int f(size_t n, int a[n])

is a handy way to document the size of an array parameter.

Standard Examples

Section 6.7.6.3 of C11 has several examples of conformant array parameters. Example 4 illustrates a variably modified parameter:

void addscalar(int n, int m,
               double a[n][n*m+300], double x);

int main()
{
  double b[4][308];
  addscalar(4, 2, b, 2.17);
  return 0;
}

void addscalar(int n, int m,
               double a[n][n*m+300], double x)
{
  for (int i = 0; i < n; i++)
  for (int j = 0, k = n*m+300; j < k; j++)
    // a is a pointer to a VLA with n*m+300 elements
    a[i][j] += x;
}

Example 5 illustrates a set of compatible function prototype declarators

double maximum(int n, int m, double a[n][m]);
double maximum(int n, int m, double a[*][*]);
double maximum(int n, int m, double a[ ][*]);
double maximum(int n, int m, double a[ ][m]);

These prototype declarators are also compatible:

void f(double (* restrict) a)[5]);
void f(double a[restrict][5]);
void f(double a[restrict 3][5]);
void f(double a[restrict static 3][5]);

C11 concludes with the following note regarding example 5:

Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a
non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.

Noncompliant Code Example

void my_memset(char* p, size_t n, char v) {
  memset( p, v, n);
}

Noncompliant Code Example

This doesn't compile because n is used before being declared.

void my_memset(char p[n], size_t n, char v) {
  memset( p, v, n);
}

Compliant Solution

void my_memset(size_t n, char p[n], char v) {
  memset( p, v, n);
}

Bibliography

C99, section 6.7.6.3 (see example 4)

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