Programming in C

File Management and Streams

• File operations: open, read, write, close using fopen, fclose, fread, fwrite, fseek, ftell.
• Streams: standard streams stdin, stdout, stderr.
• Command-line arguments: int main(int argc, char *argv[]), where argc is count and argv holds arguments.
• Error handling: check return values (e.g., fopen may return NULL), use perror or strerror(errno).
• Random access: use fseek and ftell to move and query file position for binary I/O.

FILE *fp = fopen("data.bin", "rb");
if (fp == NULL) { perror("open"); exit(1); }
char buf[128];
size_t n = fread(buf, 1, sizeof(buf), fp);
fclose(fp);

Command-line Arguments & Error Handling

• Access arguments via argv[1] etc.; convert strings to numbers with atoi, strtol.
• Always validate argc and check conversions for errors.
• Use errno, perror and return non-zero exit code on failure.

Dynamic Memory Allocation

• malloc: allocate uninitialized block: void *malloc(size_t size). Check for NULL.
• calloc: allocate and zero-initialize: void *calloc(nmemb, size).
• realloc: resize previously allocated block: void *realloc(ptr, new_size). Use carefully to avoid leaks.
• free: release memory: free(ptr). Avoid double-free and use-after-free.

int *a = malloc(n * sizeof(int));
if (a == NULL) { perror("malloc"); exit(1); }
... use a ...
free(a);

Basic Idea — Linked List

• Self-referential structure where each node points to next: struct Node { int val; struct Node *next; };.
• Create nodes with malloc, set fields, and link via pointers; free nodes when removed.
• Common ops: insert at head, delete node, traverse; watch for NULL checks.

struct Node *n = malloc(sizeof *n);
n->val = v;
n->next = head;
head = n;

Preprocessor Directives

• Macro definition: #define PI 3.14 — text substitution before compilation.
• Macro substitution: use parentheses in macros to avoid precedence bugs: #define SQR(x) ((x)*(x)).
• File inclusion: #include <stdio.h> or #include "file.h".
• Conditional compilation: #ifdef, #ifndef, #if, #endif.

#define MAX(a,b) ((a) > (b) ? (a) : (b))
int m = MAX(x, y);

Debugging Exercise

#include <stdio.h>
#include <stdlib.h>

char *make_message() {
  char buf[64];
  snprintf(buf, sizeof(buf), "hello");
  return buf; // error: returning pointer to local stack buffer
}

Programming Exercise

• Write a program that reads a binary file of integers and prints statistics (min, max, mean) using fread.
• Implement a simple singly linked list with insert and delete operations using dynamic memory.