Comparing Arrays C

Question

Is the defacto method for comparing arrays (in C) to use memcmpfrom string.h?

I want to compare int and double arrays in my unit tests

I am not sure whether to use something like:

double a[] = {1.0, 2.0, 3.0};
double b[] = {1.0, 2.0, 3.0};
size_t n = 3;
if (! memcmp(a, b, n * sizeof(double)))
    /* arrays equal */

or write a type function is_array_equal(a, b, n)to order?

Answer 1

memcmpwill make an exact comparison, which is rarely a good idea for a float and will not follow the rule NaN = NaN. For sorting, this is good, but for other purposes you can make a rough comparison, for example:

bool dbl_array_eq(double const *x, double const *y, size_t n, double eps)
{
    for (size_t i=0; i<n; i++)
        if (fabs(x[i] - y[i]) > eps)
            return false;
    return true;
}

Answer 2

Replace memsetwith memcmpin in your code and it works.

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memcmp(a, b, sizeof(a));

Answer 3

memcmp . .

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struct {
    char c;
    // 1
    int i;
    // 2
}

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

int main (void) {
    double d1 = 0.0 / 0.0, d2 = d1;

    if (d1 == d2)
        puts ("Okay");
    else
        puts ("Bad");

    if (memcmp (&d1, &d2, sizeof(double)) == 0)
        puts ("Okay");
    else puts
        ("Bad");

    return 0;
}

Bad
Okay

.

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/ d1 d2 :

 double d1 = 0.0, d2 = -d1;

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Answer 4

, , memcmp, memset. . , memcmp .

Answer 5

memcmp

memset

can be compared without using memcmp as follows. the same can be changed for different data types.

int8_t array_1[] = { 1, 2, 3, 4 }
int8_t array_2[] = { 1, 2, 3, 4 }

uint8_t i;
uint8_t compare_result = 1;

for (i = 0; i < (sizeof(array_1)/sizeof(int8_t); i++)
{
 if (array_1[i] != array_2[i])
  {
   compare_result = 0;
   break;
  }
}