C Language Input and Output Library Function Explanation (Latest Recommendation)

Input and output function: enables programs to interact with users or files.

Header file: #include<>

1. printf function: output format information to the console 💬

🔧Using format

printf("Format string", Parameter list);

🎯 Function

Output the formatted string to the console. The format string can contain ordinary characters and format specifiers, and the format specifier will be replaced by the value in the parameter list afterwards.

📖 Usage

The format specifier is generally%The beginning, the common ones are%d(for output integers),%f(for output floating point numbers),%c(for output characters),%s(used to output strings) etc.

⚠️ Notes

The format specifier should match the type of the parameter.
Normal characters in the format string will be output as is.

📌 Applicable Type

Suitable for various basic data types as well as strings.

💡 Example

#include &lt;&gt;
int main() {
    int age = 20;
    float height = 1.75;
    char grade = 'A';
    char name[] = "Alice";
    // Output integer    printf("Age is %d years old.\n", age); 
    // Output floating point number    printf("Height is %.2f meters.\n", height); 
    // Output characters    printf("The grade level is %c.\n", grade); 
    // Output string    printf("The name is %s.\n", name); 
    return 0;
}

🌟 Explain

In this example,printfThe function outputs the value of the variable to the console according to the format specifier.%.2fIndicates that two decimal places are retained when outputting floating point numbers.

2. scanf function: read formatted input from the console 📥

🔧Using format

scanf("Format string", &amp;variable1, &amp;variable2, ...);

🎯 Function

Read the data entered by the user from the console and store the data in the corresponding variable according to the requirements of the format string.

📖 Usage

Format specifier andprintfSimilar in functions, but the address character must be added before the variable name.&, to indicate that the data is to be stored at the address of the variable.

⚠️ Notes

The input data must match the format string.
When entering multiple data, it is generally separated by spaces, tabs or newlines.

📌 Applicable Type

Suitable for various basic data types.

💡 Example

#include &lt;&gt;
int main() {
    int num;
    float score;
    char ch;
    // Prompt the user to enter integer    printf("Please enter an integer:"); 
    scanf("%d", &amp;num);
    // Prompt the user to enter a floating point number    printf("Please enter a floating point number:"); 
    scanf("%f", &amp;score);
    // Prompt the user to enter characters    printf("Please enter a character:"); 
    scanf(" %c", &amp;ch); // Note the spaces in front, which are used to skip the line breaks entered before    // Output the content input by the user    printf("The integer you enter is %d, the floating point number is %.2f, and the character is %c.\n", num, score, ch); 
    return 0;
}

🌟 Explain

In this example,scanfThe function reads the user input data according to the format specifier and stores them in the corresponding variables. Adding spaces before reading characters is to skip the line breaks entered before.

3. getchar function: read a single character ⌨️

🔧Using format

int getchar(void);

🎯 Function

Read a character from standard input (usually a keyboard) and return the ASCII code value of that character.

📖 Usage

CallgetcharWhen the function is used, the program will pause and wait for the user to enter a character. After pressing the Enter key, the function will return the ASCII code value of the character.

⚠️ Notes

getcharIt can read newline characters, so you should pay attention to handling newline characters when using them continuously.
The function return value isintType, notchartype.

📌 Applicable Type

Applicable to character types.

💡 Example

#include &lt;&gt;
int main() {
    char ch;
    // Prompt the user to enter a character    printf("Please enter a character:"); 
    ch = getchar();
    // Output the characters entered by the user    printf("The character you entered is %c.\n", ch); 
    return 0;
}

🌟 Explain

In this example,getcharThe function reads a character entered by the user and assigns it to a variablech, and then output the character.

4. putchar function: output a single character 🖨️

🔧Using format

int putchar(int c);

🎯 Function

Output a character to standard output (usually the console).

📖 Usage

Pass an ASCII code value or character constant of a character, and the function will output the corresponding character to the console.

⚠️ Notes

The passed parameters can be character constants or ASCII code values of character variables.
The function returns the ASCII code value of the output character.

📌 Applicable Type

Applicable to character types.

💡 Example

#include &lt;&gt;
int main() {
    char ch = 'B';
    // Output characters    putchar(ch); 
    putchar('\n'); // Output line breaks    return 0;
}

🌟 Explain

In this example,putcharFunctions to characterBOutput to the console and output a newline character.

5. fopen function: open the file 📂

🔧Using format

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

🎯 Function

Open a file with the specified file name and return a pointer to the fileFILEPointer.

📖 Usage

filenameIt is the name of the file to be opened.modeIt is a mode for opening files. Common modes include:

"r": Open the file in read-only mode.
"w": Open the file in write mode, create it if the file does not exist, and clear the content if it exists.
"a": Open the file in append mode, and create it if the file does not exist.

⚠️ Notes

After opening the file, check whether the returned pointer isNULL, ifNULLIt means that the file is opened failed.
After operating the file, usefcloseFunction closes the file.

📌 Applicable Type

Suitable for file operations.

💡 Example

#include &lt;&gt;
int main() {
    FILE *file;
    // Open the file in read-only mode    file = fopen("", "r"); 
    if (file == NULL) {
        // Output error message        printf("Cannot open the file!\n"); 
        return 1;
    }
    // File reading operations can be performed here    // Close the file    fclose(file); 
    return 0;
}

🌟 Explain

In this example,fopenThe function tries to open in read-only modeIf the file is opened, an error message will be output. After the file is opened successfully, the file can be read. Finally, usefcloseFunction closes the file.

6. fclose function: close the file ❌

🔧Using format

int fclose(FILE *stream);

🎯 Function

Close the specified file stream and release the relevant resources.

📖 Usage

Pass in a pointerFILEA pointer of type, which is passedfopenThe function returns.

⚠️ Notes

After closing the file, you can no longer read and write the file.
A function return value of 0 indicates that the closing is successful, and non-0 indicates that the closing is failed.

📌 Applicable Type

Suitable for file operations.

💡 Example

#include &lt;&gt;
int main() {
    FILE *file;
    // Open the file in write mode    file = fopen("", "w"); 
    if (file == NULL) {
        // Output error message        printf("Cannot open the file!\n"); 
        return 1;
    }
    // File writing operations can be performed here    // Close the file    if (fclose(file) == 0) {
        printf("File close successfully!\n");
    } else {
        printf("File closing failed!\n");
    }
    return 0;
}

🌟 Explain

In this example,fopenThe function is opened in write modeFile, after file writing operation, usefcloseThe function closes the file and judges whether the closing is successful based on the return value.

7. fgets function: safely read strings 📃

🔧Using format

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

🎯 Function

Read a line of string from the specified file stream and store it tostrpointing to the character array.

📖 Usage

stris a character array that stores read strings.nis the maximum number of characters to read (including line breaks and string ending characters'\0'），streamIt is a file stream pointer, which can bestdin(standard input) or viafopenOpen file pointer.

⚠️ Notes

If the number of characters read reachesn - 1Or when encountering a newline, the reading will stop and will be added at the end of the string.'\0'。
If the reading is successful, returnstrPointer; if the file ending character or error occurs, returnNULL。

📌 Applicable Type

Applicable to string types.

💡 Example

#include &lt;&gt;
int main() {
    char buffer[100];
    // Read a line of string from standard input    printf("Please enter a string:"); 
    fgets(buffer, sizeof(buffer), stdin);
    // Output the read string    printf("The string you entered is: %s", buffer); 
    return 0;
}

🌟 Explain

In this example,fgetsFunctions read a line of string from standard input, at mostsizeof(buffer) - 1character and then store it tobufferIn the array and output the string.

8. fputs function: output string to file 📤

🔧Using format

int fputs(const char *str, FILE *stream);

🎯 Function

Put stringstrOutput to the specified file stream.

📖 Usage

stris the string to be output,streamIt is a file stream pointer, which can bestdout(standard output) or viafopenOpen file pointer.

⚠️ Notes

The function will not automatically add newline characters. If a newline is required, add it manually in the string.'\n'。
If the output is successful, return a non-negative value; if an error occurs, returnEOF。

📌 Applicable Type

Applicable to string types.

💡 Example

#include &lt;&gt;
int main() {
    FILE *file;
    // Open the file in write mode    file = fopen("", "w"); 
    if (file == NULL) {
        // Output error message        printf("Cannot open the file!\n"); 
        return 1;
    }
    // Write strings to the file    fputs("Hello, World!\n", file); 
    // Close the file    fclose(file); 
    return 0;
}

🌟 Explain

In this example,fopenThe function is opened in write modedocument,fputsFunctions put strings"Hello, World!\n"Write to the file and finally usefcloseFunction closes the file.

Buffer management skills

General clearing solution：

void clear_buffer() {
    int c;
    while ((c = getchar()) != '\n' && c != EOF);
}

Use scenarios：

existscanf()Call it immediately afterward

When handling exception input

💡 Golden Rule：

All input functions must consider the risk of buffer overflow
After the file operation, you must check the return value and close the file
Format IO must strictly match the type

By mastering these core functions, your C language IO operation will be easy! 🎯

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