C Notes
HubApplications of C Programming LanguageFeatures of C Programming LanguageHistory of C Programming LanguageWhat is C Language?Why Learn C Programming in 2024?First C Program - Hello World in C with ExplanationGCC Compiler - Complete Guide to GNU C CompilerInstall C Compiler on Linux - GCC Setup Guide for All DistrosInstall C Compiler on macOS - Xcode Command Line Tools and Homebrew GCCInstall C Compiler on Windows - MinGW, MSYS2, and WSL GuideSetup VS Code for C Programming - Complete Configuration GuideC Syntax Rules — Complete GuideComments in C ProgrammingConstants in C ProgrammingData Types in CIdentifiers in C ProgrammingKeywords in C ProgrammingStructure of a C ProgramVariables in C ProgrammingArithmetic Operators in C ProgrammingAssignment Operators in C ProgrammingBitwise Operators in C ProgrammingIncrement and Decrement Operators in CLogical Operators in C ProgrammingRelational Operators in C ProgrammingTernary Operator in C ProgrammingBreak Statement in C ProgrammingContinue Statement in C ProgrammingDo-While Loop in C ProgrammingFor Loop in C ProgrammingGoto Statement in C Programmingif-else Statement in C Programmingif Statement in C ProgrammingNested if Statements in C ProgrammingSwitch Statement in C ProgrammingWhile Loop in C ProgrammingFunction Arguments in C - Pass by Value vs Pass by ReferenceFunction Call in C ProgrammingFunction Declaration (Prototype) in CFunction Definition in C ProgrammingIntroduction to Functions in C ProgrammingRecursion in C ProgrammingReturn Statement in C ProgrammingStorage Classes in C ProgrammingArray Operations in C - Searching, Sorting, Insert and DeleteArray Programs in C - Reverse, Rotate, Duplicates, MergeIntroduction to Arrays in C ProgrammingMultidimensional Arrays in C ProgrammingOne Dimensional Arrays in C ProgrammingPassing Arrays to Functions in CTwo Dimensional Arrays in C ProgrammingString Comparison in C - strcmp, strncmp, Case-InsensitiveString Functions in C - strlen, strcpy, strcat, strcmpC String Handling Library - Complete string.h ReferenceString Manipulation in C - Reverse, Uppercase, PalindromeString Programs in C - Anagram, Word Count, Vowels, FrequencyStrings in C Programming - Complete IntroductionDouble Pointers in C - Pointer to PointerPointer Arithmetic in C ProgrammingPointer Declaration and Initialization in CPointer Programs in C - Swap, String Reversal, Dynamic AllocationPointers and Arrays in C - The Relationship ExplainedPointers and Functions in C - Pass by ReferenceIntroduction to Pointers in C ProgrammingVoid Pointers in C - Generic Pointers Guidecalloc() in C – Contiguous Memory AllocationDynamic Arrays in C – Runtime-Sized Arraysfree() in C – Releasing Dynamic Memorymalloc() in C – Dynamic Memory AllocationMemory Management Best Practices in Crealloc() in C – Resizing Dynamic MemoryBinary Files in C – fread and fwriteFile Handling in C – IntroductionFile Handling Projects in C – Student Records & Phone BookFile Modes in C – Complete Guidefopen() and fclose() in C – Opening and Closing FilesReading Files in C – fgetc, fgets, fscanf, freadWriting Files in C – fputc, fputs, fprintf, fwriteConditional Compilation in C – #ifdef, #ifndef, #if#define Macros in C – Constants and Macro FunctionsHeader Files in C – Creating Custom Headers#include Directive in C – File InclusionMacro Functions in C – Parameterized MacrosC Preprocessor – Overview and DirectivesGraphs in C – Adjacency Matrix, Adjacency List, BFS, and DFSHash Tables in C – Implementation, Collision Handling, and ChainingLinked List in C – Singly, Doubly, and Circular with ImplementationQueue in C – Linear, Circular, and Priority Queue ImplementationStack in C – Array and Linked List Implementation with ApplicationsTrees in C – Binary Search Tree Implementation with TraversalsC Programming Best Practices – Coding Standards, Safety, and PerformanceBit Fields in C – Definition, Use Cases, and Protocol HeadersC Standard Library Overview – All Headers and Common FunctionsCommand Line Arguments in C – argc and argv ExplainedDebugging Techniques in C – GDB, Valgrind, and SanitizersFunction Pointers in C – Complete Guide with ExamplesMemory Layout of a C Program – Text, Data, BSS, Heap, StackBank Management System in C – Complete Project with File StorageFile Encryption Tool in C – XOR Cipher ImplementationLibrary Management System in C – Complete Project with Source CodeMini Compiler in C – Lexer and Parser for Simple ExpressionsSnake Game in C – Console-Based Game with Source CodeStudent Management System in C – Complete Project with Source CodeC Programming Cheatsheet – Complete Quick Reference GuideTop 50 C Programming Interview Questions with Answers (2025)Memory Management Interview Questions in C with AnswersOutput Prediction Questions in C – What Will This Program Print?Pointer Interview Questions in C – Tricky Problems with AnswersCommon C Programming Errors and Solutions – Debugging GuideImportant C Programs – 50+ Frequently Asked Programs with SolutionsQuick Revision Notes for C Programming – Complete C in 10 MinutesRecommended C Programming Books – From Beginner to ExpertFormat Specifiers in C - Complete Referencegetchar() and putchar() in C Programminggets() and puts() in C ProgrammingC Input Output Programs and Examplesprintf() Function in C Programmingscanf() Function in C ProgrammingArrays of Structures in C – Managing CollectionsEnums in C – Enumerated Data TypesNested Structures in C – Struct Within StructPointers to Structures in C – Arrow OperatorStructures in C – User-Defined Data Typestypedef in C – Creating Type AliasesUnions in C – Shared Memory Data Types
Complete guide to reading files in C — character-by-character with fgetc, line-by-line with fgets, formatted reading with fscanf, block reading with fread, practical examples with output.
C provides multiple ways to read from files, each suited to different situations. Need one character at a time? Use fgetc(). Want a whole line? Use fgets(). Need structured data? Use fscanf(). Working with binary? Use fread(). Let's explore each one.
File Reading Functions Overview
| Function | Reads | Best For |
|---|---|---|
fgetc() | One character | Character-by-character processing |
fgets() | One line (up to n chars) | Line-by-line text processing |
fscanf() | Formatted data | Structured text (like CSV) |
fread() | Binary block | Structs, arrays, binary data |
fgetc() — Reading One Character at a Time
c example
int fgetc(FILE *stream);
// Returns: character read (as int), or EOF on end/errorExample
#include <stdio.h>
int main() {
FILE *fp = fopen("sample.txt", "r");
if (fp == NULL) {
printf("Cannot open file\n");
return 1;
}
int ch;
int char_count = 0, line_count = 0;
while ((ch = fgetc(fp)) != EOF) {
char_count++;
if (ch == '\n') line_count++;
putchar(ch); // Print to screen
}
printf("\n--- Stats: %d characters, %d lines ---\n", char_count, line_count);
fclose(fp);
return 0;
}
Output
Hello World This is line 2 End of file --- Stats: 35 characters, 3 lines ---
fgets() — Reading Line by Line (Recommended)
c example
char *fgets(char *str, int n, FILE *stream);
// Reads at most n-1 characters or until newline/EOF
// Returns: str on success, NULL on EOF/errorExample
#include <stdio.h>
int main() {
FILE *fp = fopen("poem.txt", "r");
if (fp == NULL) return 1;
char line[256];
int line_num = 1;
while (fgets(line, sizeof(line), fp) != NULL) {
printf("%3d | %s", line_num++, line);
}
fclose(fp);
return 0;
}
Output
1 | Roses are red, 2 | Violets are blue, 3 | C is amazing, 4 | And so are you!
Note: fgets() includes the newline \n in the buffer if it fits.
Removing the Trailing Newline
Example
#include <stdio.h>
#include <string.h>
int main() {
FILE *fp = fopen("names.txt", "r");
if (fp == NULL) return 1;
char name[100];
while (fgets(name, sizeof(name), fp)) {
// Remove trailing newline
name[strcspn(name, "\n")] = '\0';
printf("Name: [%s]\n", name);
}
fclose(fp);
return 0;
}
Output
Name: [Alice] Name: [Bob] Name: [Charlie]
fscanf() — Formatted Reading
c example
int fscanf(FILE *stream, const char *format, ...);
// Returns: number of items successfully read, or EOFExample
#include <stdio.h>
int main() {
FILE *fp = fopen("students.txt", "r");
if (fp == NULL) return 1;
// File contains: "101 Alice 92.5" per line
int roll;
char name[50];
float marks;
printf("%-5s %-10s %s\n", "Roll", "Name", "Marks");
printf("───────────────────────\n");
while (fscanf(fp, "%d %s %f", &roll, name, &marks) == 3) {
printf("%-5d %-10s %.1f\n", roll, name, marks);
}
fclose(fp);
return 0;
}
Output
Roll Name Marks ─────────────────────── 101 Alice 92.5 102 Bob 88.0 103 Charlie 95.3
fread() — Binary Block Reading
c example
size_t fread(void *ptr, size_t size, size_t count, FILE *stream);
// Returns: number of items successfully readExample
#include <stdio.h>
struct Record {
int id;
char name[30];
double salary;
};
int main() {
FILE *fp = fopen("employees.dat", "rb");
if (fp == NULL) {
printf("Cannot open binary file\n");
return 1;
}
struct Record rec;
printf("%-5s %-15s %s\n", "ID", "Name", "Salary");
while (fread(&rec, sizeof(struct Record), 1, fp) == 1) {
printf("%-5d %-15s %.2f\n", rec.id, rec.name, rec.salary);
}
fclose(fp);
return 0;
}
Output
ID Name Salary 1 Alice 75000.00 2 Bob 68000.00 3 Charlie 82000.00
Reading Entire File into a String
Example
#include <stdio.h>
#include <stdlib.h>
char *read_entire_file(const char *filename) {
FILE *fp = fopen(filename, "r");
if (fp == NULL) return NULL;
// Get file size
fseek(fp, 0, SEEK_END);
long size = ftell(fp);
rewind(fp);
// Allocate buffer
char *buffer = (char *)malloc(size + 1);
if (buffer == NULL) {
fclose(fp);
return NULL;
}
// Read entire file
size_t read = fread(buffer, 1, size, fp);
buffer[read] = '\0';
fclose(fp);
return buffer;
}
int main() {
char *content = read_entire_file("config.txt");
if (content != NULL) {
printf("File contents:\n%s\n", content);
free(content);
}
return 0;
}
Reading CSV Data
Example
#include <stdio.h>
#include <string.h>
int main() {
FILE *fp = fopen("data.csv", "r");
if (fp == NULL) return 1;
char line[256];
// Skip header
fgets(line, sizeof(line), fp);
printf("Parsed CSV data:\n");
while (fgets(line, sizeof(line), fp)) {
char name[50];
int age;
float score;
if (sscanf(line, "%[^,],%d,%f", name, &age, &score) == 3) {
printf(" Name: %-10s Age: %d Score: %.1f\n", name, age, score);
}
}
fclose(fp);
return 0;
}
Output
Parsed CSV data: Name: Alice Age: 20 Score: 92.5 Name: Bob Age: 22 Score: 85.0 Name: Charlie Age: 21 Score: 91.3
Comparison: Which Function to Use?
| Scenario | Function | Why |
|---|---|---|
| Count characters | fgetc() | Process each character |
| Display file content | fgets() | Line by line is natural |
| Parse structured text | fscanf() | Format string handles parsing |
| Load binary struct | fread() | Reads exact byte count |
| Read CSV/TSV | fgets() + sscanf() | More control over line parsing |
| Read entire small file | fread() | One call, entire content |
Interview Questions
Q1: Why does fgetc() return int instead of char?
Because EOF is defined as -1 (or another negative value), which can't be represented by char on systems where char is unsigned. Returning int allows distinguishing between a valid character (0-255) and EOF (-1).
Q2: What's safer — fgets() or gets()?
fgets() is always safer because it takes a size limit parameter, preventing buffer overflow. gets() has no size limit and is so dangerous that it was removed from the C11 standard entirely. Never use gets().
Q3: What does fscanf() return?
It returns the number of items successfully read and assigned, or EOF if end-of-file is reached before any conversion. Always check the return value to detect incomplete reads.
Q4: How do you detect end-of-file correctly?
Use the return value of the reading function (NULL from fgets, EOF from fgetc, 0 from fread) rather than calling feof() before reading. The feof() function only returns true AFTER a read has already failed.
Summary
fgetc()— read one character, returns EOF when donefgets()— read a line safely (always specify buffer size)fscanf()— read formatted data (check return value!)fread()— read binary blocks of exact size- Always check return values to detect EOF and errors
- Prefer
fgets()overgets()(gets is removed from C11) - For CSV parsing, combine
fgets()withsscanf()orstrtok()
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for Reading Files in C – fgetc, fgets, fscanf, fread.
Interview Use
Prepare one clear explanation, one practical example, and one common mistake for this C Programming topic.
Search Terms
c-programming, c programming, programming, file, handling, reading, files, reading files in c – fgetc, fgets, fscanf, fread
Related C Programming Topics
Continue learning this concept
File HandlingBinary Files in C – fread and fwriteComplete guide to binary file handling in C — reading and writing binary data with fread/fwrite, struct serialization, random access with fseek, database-like operations, practical examples.File Handlingfopen() and fclose() in C – Opening and Closing FilesComplete guide to fopen() and fclose() in C — file opening modes, error checking, file paths, buffering, practical examples with output, and best practices for file management.File HandlingWriting Files in C – fputc, fputs, fprintf, fwriteComplete guide to writing files in C — character writing with fputc, string writing with fputs, formatted output with fprintf, binary writing with fwrite, practical examples with output.File HandlingFile Handling in C – IntroductionComplete introduction to file handling in C programming — what are files, why file I/O is needed, types of files (text vs binary), file operations overview, streams, FILE pointer concept with examples.File HandlingFile Handling Projects in C – Student Records & Phone BookComplete file handling project examples in C — student record management system, phone book application with add/search/delete/display operations, menu-driven programs with binary files.File HandlingFile Modes in C – Complete GuideComplete guide to file modes in C — r, w, a, r+, w+, a+ modes, binary modes rb/wb/ab, mode comparison table, choosing the right mode, practical examples with output.