Insert into an array with spare capacity.
C: Move the trailing elements before inserting and keep the logical length separate from capacity.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <stdint.h>
#include <stdbool.h>
#include <errno.h>
#include <limits.h>
#include <math.h>
#include <time.h>
int main(void) {
int values[5] = {1,3,4};
size_t length=3,index=1;
if (length >= sizeof values/sizeof values[0] || index>length) return 1;
memmove(values+index+1,values+index,(length-index)*sizeof values[0]);
values[index]=2;
length++;
for (size_t i=0;i<length;i++) printf("%d\n",values[i]);
return 0;
}Expected output EXAMPLE
1 2 3 4
Details
Save as snippet.c; compile with gcc -std=c17 -Wall -Wextra snippet.c -lm -o snippet, then run ./snippet. Move the trailing elements before inserting and keep the logical length separate from capacity.
Tested on Ubuntu 24.04.5 LTS · · gcc (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0 · gcc 4:13.2.0-7ubuntu1
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Unprivileged snippet process, external networking disabled, read-only root filesystem, and a fresh temporary working directory. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged) / C.UTF-8
- Interpreter invocation
gcc -std=c17 -Wall -Wextra -Werror snippet.c -lm -o snippet && ./snippet- Container image ID
sha256:32dc2d998158b6554c99b73b533f423696a0f3e31e8cbea9db10b5eee9a2fadd- Code SHA-256
a7d5f8b032b67d61cfe04af3c1a6c29e1d9647e1a6a5af9c8fa27335c4dc7cd9- Dependencies
- gcc 4:13.2.0-7ubuntu1
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
# No input files required.
Observed standard output
1 2 3 4
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.