Back CSE 240 Module 4: Advanced C Programming Programming
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CSE 240 Module 4: Advanced C Programming

CSE 240 Module 4: Advanced C Programming




CSE 240 Module 4

Advanced C Programming: Memory, Files, and Data Structures



Module 4 Topics


Structure Padding

File I/O

Buffer Management

Parameter Passing

Linked Lists

Glossary







Structure Padding & Memory Layout


The compiler adds padding bytes between structure members to ensure proper memory alignment for efficient access. Understanding this is crucial for memory optimization and avoiding bugs.


Memory Alignment Rules

Most systems require data to be aligned on boundaries equal to their size:


char: 1-byte alignment (no padding needed)

short: 2-byte alignment

int/float: 4-byte alignment

double/long long: 8-byte alignment



Example: Poor vs Good Structure Design


// Poor design - lots of padding
struct bad_example {
char a; // 1 byte
// 3 bytes padding
int b; // 4 bytes
char c; // 1 byte
// 7 bytes padding
double d; // 8 bytes
}; // Total: 24 bytes

// Better design - minimized padding
struct good_example {
double d; // 8 bytes
int b; // 4 bytes
char a; // 1 byte
char c; // 1 byte
// 2 bytes padding
}; // Total: 16 bytes




Memory Layout Visualization:

Bad Structure (24 bytes):
a___bbbbc_______dddddddd

Good Structure (16 bytes):
ddddddddbbbbac__




Tip: Use `sizeof()` to check actual structure sizes and `offsetof()` from stddef.h to see member positions.



Packed Structures


// Force no padding (compiler-specific)
#pragma pack(1)
struct packed_struct {
char a;
int b;
char c;
}; // Exactly 6 bytes, but slower access
#pragma pack()

// Or use __attribute__((packed)) with GCC
struct packed_struct2 {
char a;
int b;
char c;
} __attribute__((packed));






File I/O Operations


C provides both high-level (stdio.h) and low-level file operations.…