C Program Memory Layout

1#include <stdio.h>
2
3// All this code goes to TEXT segment
4int add(int a, int b) {
5    return a + b;  // Instructions stored in TEXT
6}
7
8int main() {
9    int result = add(5, 3);  // Call instruction in TEXT
10    printf("Sum: %d\n", result);
11    return 0;
12}

1#include <stdio.h>
2
3// Global initialized variables → DATA segment
4int playerScore = 500;
5char *gameName = "Space Invaders";
6const int MAX_LIVES = 3;
7
8int main() {
9    // Static initialized variable → DATA segment
10    static int level = 1;
11    
12    printf("Game: %s\n", gameName);
13    printf("Score: %d, Level: %d\n", playerScore, level);
14    printf("Max Lives: %d\n", MAX_LIVES);
15    
16    return 0;
17}

1#include <stdio.h>
2
3// Uninitialized global → BSS (auto-initialized to 0)
4int totalUsers;
5char username[50];
6float balance;
7
8int main() {
9    // Uninitialized static → BSS (auto-initialized to 0)
10    static int loginCount;
11    
12    printf("Total Users: %d\n", totalUsers);    // 0
13    printf("Login Count: %d\n", loginCount);    // 0
14    printf("Balance: %.2f\n", balance);         // 0.00
15    
16    // Empty string (first char is '\0')
17    printf("Username: '%s'\n", username);
18    
19    return 0;
20}

1#include <stdio.h>
2#include <stdlib.h>
3
4int main() {
5    // Allocate array on HEAP
6    int *scores = (int *)malloc(3 * sizeof(int));
7    
8    if (scores == NULL) {
9        printf("Memory allocation failed!\n");
10        return 1;
11    }
12    
13    // Use heap memory
14    scores[0] = 85;
15    scores[1] = 92;
16    scores[2] = 78;
17    
18    printf("Scores: %d, %d, %d\n", scores[0], scores[1], scores[2]);
19    
20    // Free heap memory
21    free(scores);
22    scores = NULL;
23    
24    return 0;
25}

1#include <stdio.h>
2
3void greet(char *name, int age) {
4    // name and age are on STACK (parameters)
5    char message[50];  // Local array on STACK
6    
7    printf("Hello %s, you are %d years old!\n", name, age);
8}
9
10int main() {
11    int year = 2024;       // Local variable on STACK
12    char city[] = "NYC";   // Local array on STACK
13    
14    greet("Alice", 25);    // New stack frame created
15    
16    // After greet() returns, its stack frame is removed
17    printf("Year: %d, City: %s\n", year, city);
18    
19    return 0;
20}

1# Compile the program
2gcc program.c -o program
3
4# Check segment sizes
5size program
6
7# Output example:
8#    text    data     bss     dec     hex filename
9#    1418     544       8    1970     7b2 program

1#include <stdio.h>
2#include <stdlib.h>
3
4// DATA segment (initialized globals)
5int maxPlayers = 4;
6const char *version = "1.0";
7
8// BSS segment (uninitialized globals)
9int highScore;
10char playerName[20];
11
12void showInfo(int level) {
13    // STACK: level parameter, bonus local variable
14    int bonus = level * 100;
15    printf("Level %d bonus: %d\n", level, bonus);
16}
17
18int main() {
19    // STACK: local variables
20    int currentLevel = 5;
21    
22    // HEAP: dynamic allocation
23    int *inventory = (int *)malloc(10 * sizeof(int));
24    
25    printf("=== Memory Segments Demo ===\n");
26    printf("Max Players: %d (DATA)\n", maxPlayers);
27    printf("High Score: %d (BSS, auto=0)\n", highScore);
28    
29    showInfo(currentLevel);
30    
31    // Clean up heap
32    free(inventory);
33    
34    return 0;
35}