C Standard Input and Output Library Reference

The C Standard Input and Output Library, also known as stdio.h, is an essential part of the C programming language. It provides functions to perform input and output operations, which are fundamental for any interaction a program has with users or files. Understanding how to effectively use these functions is crucial for manipulating data, receiving user input, and displaying results in a user-friendly manner.

I. Introduction to C Standard Input and Output

A. Overview of the stdio.h library

The stdio.h library includes functions for handling standard input and output operations, allowing us to read user data and print information to the console. Some of the main functions derived from this library are those used for reading from keyboard inputs and writing to the terminal or files.

B. Importance of input and output in C programming

In C programming, effective input and output mechanisms are vital. They allow programs to interact with users, handle files, and display processed data. Mastering these functions is the foundation for developing advanced C applications.

II. Input Functions

A. scanf

scanf is used to read formatted input from the standard input (keyboard).

Syntax	int scanf(const char *format, …);

Example:

#include 

int main() {
    int num;
    printf("Enter an integer: ");
    scanf("%d", &num);
    printf("You entered: %d\n", num);
    return 0;
}

B. getc

getc reads a character from a file stream.

Syntax	int getc(FILE *stream);

Example:

#include 

int main() {
    FILE *fp = fopen("file.txt", "r");
    char c;
    if (fp) {
        while ((c = getc(fp)) != EOF) {
            putchar(c);
        }
        fclose(fp);
    }
    return 0;
}

C. getchar

getchar reads the next available character from standard input.

Syntax	int getchar(void);

Example:

#include 

int main() {
    char c;
    printf("Enter a character: ");
    c = getchar();
    printf("You entered: %c\n", c);
    return 0;
}

D. fscanf

fscanf is similar to scanf but reads from a file.

Syntax	int fscanf(FILE *stream, const char *format, …);

Example:

#include 

int main() {
    FILE *fp = fopen("data.txt", "r");
    int num;
    if (fp) {
        fscanf(fp, "%d", &num);
        printf("Read number: %d\n", num);
        fclose(fp);
    }
    return 0;
}

E. gets

gets reads a line from standard input into a buffer.

Syntax	char *gets(char *str);

Note: gets() is unsafe and has been removed in C11.

F. fgets

fgets reads a line from the specified input stream.

Syntax	char *fgets(char *str, int n, FILE *stream);

Example:

#include 

int main() {
    char buffer[100];
    printf("Enter a line: ");
    fgets(buffer, 100, stdin);
    printf("You entered: %s", buffer);
    return 0;
}

III. Output Functions

A. printf

printf outputs formatted data to the standard output (console).

Syntax	int printf(const char *format, …);

Example:

#include 

int main() {
    int num = 10;
    printf("The number is: %d\n", num);
    return 0;
}

B. putc

putc writes a character to a file stream.

Syntax	int putc(int char, FILE *stream);

Example:

#include 

int main() {
    FILE *fp = fopen("output.txt", "w");
    if (fp) {
        putc('A', fp);
        fclose(fp);
    }
    return 0;
}

C. putchar

putchar writes a single character to the standard output.

Syntax	int putchar(int char);

Example:

#include 

int main() {
    putchar('B');
    putchar('\n');
    return 0;
}

D. fprintf

fprintf sends formatted output to a file stream.

Syntax	int fprintf(FILE *stream, const char *format, …);

Example:

#include 

int main() {
    FILE *fp = fopen("output.txt", "w");
    if (fp) {
        fprintf(fp, "Hello, world!\n");
        fclose(fp);
    }
    return 0;
}

E. puts

puts writes a string to the standard output with a newline.

Syntax	int puts(const char *str);

Example:

#include 

int main() {
    puts("Hello, world!");
    return 0;
}

F. fwrite

fwrite writes data from an array to a file stream.

Syntax	size_t fwrite(const void *ptr, size_t size, size_t count, FILE *stream);

Example:

#include 

int main() {
    FILE *fp = fopen("data.bin", "wb");
    int arr[5] = {1, 2, 3, 4, 5};
    fwrite(arr, sizeof(int), 5, fp);
    fclose(fp);
    return 0;
}

IV. File Operations

A. File Pointers

1. Definition

A file pointer is a pointer type variable that holds the address of a file. It allows for reading from and writing to files.

2. Syntax and usage

FILE *filePointer;

B. Opening and Closing Files

1. fopen

fopen is used to open a file and returns a file pointer.

Syntax	FILE *fopen(const char *filename, const char *mode);

Example:

#include 

int main() {
    FILE *fp = fopen("test.txt", "w");
    if (fp) {
        // file operations here
        fclose(fp);
    }
    return 0;
}

2. fclose

fclose is used to close an opened file.

Syntax	int fclose(FILE *stream);

C. Reading and Writing Files

1. fread

fread reads data from a file into an array.

Syntax	size_t fread(void *ptr, size_t size, size_t count, FILE *stream);

Example:

#include 

int main() {
    FILE *fp = fopen("data.bin", "rb");
    int arr[5];
    fread(arr, sizeof(int), 5, fp);
    fclose(fp);
    return 0;
}

2. fwrite

As mentioned previously, fwrite writes data from an array to a file.

Refer to the earlier example of fwrite for illustration.

FAQs

• Q: What is the purpose of the stdio.h library?
• A: It provides functions for input and output operations in C programming.
• Q: What is the difference between scanf and fgets?
• A: scanf reads formatted input, while fgets reads a whole line including spaces.
• Q: Why is gets unsafe?
• A: It does not perform bounds checking, which can lead to buffer overflows.
• Q: How do I open a file for reading?
• A: Use fopen with mode “r”.