C putchar Explained: Usage, Examples, Differences, FAQ

1. Introduction

2. Basic Specification of putchar

int putchar(int c);

3. Basic Usage of putchar – Code Example

#include <stdio.h>

int main(void) {
    putchar('A');
    return 0;
}

putchar('A');    // display A on screen
putchar('n');   // output newline
putchar('t');   // output tab

putchar(65);  // 65 is the ASCII code for 'A'
putchar(10);  // 10 is the ASCII code for newline ('\n')

4. Advanced examples combined with loops and arrays

#include <stdio.h>

int main(void) {
    for (int c = 'A'; c <= 'Z'; c++) {
        putchar(c);
    }
    putchar('n'); // Insert a newline at the end
    return 0;
}

#include <stdio.h>

int main(void) {
    char str[] = "Hello, world!";
    int i = 0;
    while (str[i] != '�') {
        putchar(str[i]);
        i++;
    }
    putchar('n');
    return 0;
}

#include <stdio.h>

int main(void) {
    int c;
    while ((c = getchar()) != EOF) {
        putchar(c);
    }
    return 0;
}

5. Differences and How to Choose Between printf and puts

• putchar(c) is a function that simply outputs exactly one character.
• printf("%c", c) uses format specifiers, so it can handle a wide range of uses beyond a single character (such as numbers or strings). However, because printf has more complex internal processing, putchar is more efficient when the sole purpose is to output a single character.

putchar('A');         // Simple and fast
printf("%c", 'A');   // Requires format specifier (more versatile but slightly slower)

• puts outputs the entire string (char array or literal) and automatically adds a newline.
• On the other hand, putchar can only output one character. To display an entire string, you need to use a loop to output one character at a time.

puts("Hello");    // Hello (output with newline)
putchar('H');
putchar('e');
putchar('l');
putchar('l');
putchar('o');
putchar('n');    // Same output result but more effort

• putchar: Ideal when you want to output a single character simply. Also fast when used in a loop.
• printf: Useful when you need formatting or want to output numbers or multiple values together.
• puts: Recommended when you want to output a string as is and also add a newline.

6. Benefits of Using putchar & Practical Scenarios

• When you want to process character arrays or strings one character at a time
• When you need to react to each character from standard input. It shines in such cases. For example, when you want to echo user input character by character, or when you need to process data one byte at a time.

• Outputting large amounts of data in loops
• Checking or debugging data byte by byte, etc. It is used for such purposes. In actual standard output speed comparisons, putchar is often faster than printf, making it preferred for performance‑critical programs.

7. Performance, Macro Expansion, and Caveats

putchar(c++);

if (putchar('A') == EOF) {
    // error handling
}

8. OS and Development Environment Specific Considerations

• UNIX/Linux: Line breaks are represented only by “n”.
• Windows: Line breaks are typically represented by the two characters “rn” (carriage return + line feed).

• Alphanumeric characters and half‑width symbols (i.e., single‑byte characters) can be output without issues.
• Conversely, Japanese text and certain symbols (those that become two or more bytes in UTF‑8, Shift_JIS, etc.) may not be representable with a single putchar call.

• Because standard output is buffered, output may not appear on the screen immediately
• It may be necessary to explicitly flush the buffer with fflush(stdout);

• #include <wchar.h>
• A program locale must be set (using functions such as setlocale).

#include <wchar.h>
#include <locale.h>

int main(void) {
    setlocale(LC_ALL, "");
    putwchar(L'漢');
    return 0;
}

9. Common Misconceptions and Trouble Cases

putchar("Hello");

10. Frequently Asked Questions (FAQ)

• puts outputs an entire string and automatically appends a newline, making it convenient for string output.
• fputc is similar to putchar, but it can write to any FILE pointer. Use fputc when you want to output one character at a time to something other than standard output (e.g., a file or another stream).

11. Summary

12. Reference Links & Official Documentation

• cppreference.com C Standard Library Reference (putchar)
• Linux man page (putchar(3))

• Dotinstall “C Language Introduction”
• paiza Learning C Language Intro Course
• AtCoder Programming Guide for Beginners (APG4b)

• “New Clear C Language: Introductory Edition” (Mochi Shibata, SB Creative)

• The behavior and fine details of standard library functions may vary slightly depending on the compiler and OS. It is reliable to learn by verifying the behavior in your own development environment.
• You can also check other I/O functions (fputc, putwchar, printf, puts, etc.) via the reference links.