C programming/Variable Lengt Arrays VLA - Revision history

Heth at 06:02, 1 December 2022

2022-12-01T06:02:55Z

Heth: /* Problems */

2022-12-01T06:02:39Z

‎Problems

Heth at 06:01, 1 December 2022

2022-12-01T06:01:59Z

Heth at 05:57, 1 December 2022

2022-12-01T05:57:47Z

Heth: Created page with "From C99 variable length arrays was introduced in c. #include #include float process(int n, float *vals) { for (int i=0; i..."

2022-12-01T05:57:07Z

Created page with "From C99 variable length arrays was introduced in c. <source lang=c line> #include <stdio.h> #include <stdlib.h> float process(int n, float *vals) { for (int i=0; i..."

New page

From C99 variable length arrays was introduced in c.
<source lang=c line>
#include <stdio.h>
#include <stdlib.h>

float process(int n, float *vals) {
for (int i=0; i < n; i++) {
printf("%f ", vals[i]);
}
printf("\n");
}

float read_and_process_vla(int n) {
float vals[n];
for (int i = 0; i < n; ++i)
vals[i] = i;
return process(n, vals);
}

float read_and_process_novla(int n) {
float (*vals)[n] = malloc(sizeof(float[n]));
for (int i = 0; i < n; ++i)
(*vals)[i] = i;
float ret = process(n, *vals);
free(vals);
return ret;
}
int main(void) {
printf("========================= Using VLA =========================\n");
read_and_process_vla(10);
read_and_process_vla(20);
//read_and_process_vla(10000000);
printf("======================= not using VLA =======================\n");
read_and_process_novla(10);
read_and_process_novla(20);
read_and_process_novla(10000000);
return(0);
}
</source>

← Older revision		Revision as of 06:02, 1 December 2022
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	}		}
	</source>		</source>
		+	[[Category:C]]

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 ==Problems==
 VLA use the stack as placeholder for the array:
-*In the function ''read_and_process_vla()'' - the stack is used as storage for the array. If the array is greather than the remaining stack size - stack overflow occurs. Check stack size on Linux with '''ulimit -a'''
+*In the function '''read_and_process_vla()''' - the stack is used as storage for the array. If the array is greather than the remaining stack size - stack overflow occurs. Check stack size on Linux with the '''ulimit -a''' command
-*In the function ''read_and_process_novla()'' - the heap through ''malloc()'' is used.
+*In the function '''read_and_process_novla()''' - the heap through '''malloc()''' is used.
 Be careful when using VLA

@@ Line 1: / Line 1: @@
 From C99 variable length arrays was introduced in c.
 <source lang=c line>
 #include <stdio.h>

@@ Line 31: / Line 31: @@
          read_and_process_vla(10);
          read_and_process_vla(20);
-         //read_and_process_vla(10000000);
+         //read_and_process_vla(10000000); // Error if stacksize not big enough...
          printf("======================= not using VLA =======================\n");
          read_and_process_novla(10);