stdio.h

Overview

stdio.h大致内容[1]

Functions

printf

/* printout.c -- uses conversion specifiers */
#include <stdio.h>
#define PI 3.141593
int main(void)
{
    int number = 7;
    float pies = 12.75;
    int cost = 7800;

    printf("The %d contestants ate %f berry pies.\n", number,
           pies);
    printf("The value of pi is %f.\n", PI);
    printf("Farewell! thou art too dear for my possessing,\n");
    printf("%c%d\n", '$', 2 * cost);

    return 0;
}

// The 7 contestants ate 12.750000 berry pies.
// The value of pi is 3.141593.
// Farewell! thou art too dear for my possessing,
// $15600

/* varwid.c -- uses variable-width output field */
#include <stdio.h>
int main(void)
{
    unsigned width, precision;
    int number = 256;
    double weight = 242.5;

    printf("Enter a field width:\n");
    scanf("%d", &width);
    printf("The number is :%*d:\n", width, number);
    printf("Now enter a width and a precision:\n");
    scanf("%d %d", &width, &precision);
    printf("Weight = %*.*f\n", width, precision, weight);
    printf("Done!\n");

    return 0;
}

// Enter a field width:
// 10
// The number is :       256:
// Now enter a width and a precision:
// 10 3
// Weight =    242.500
// Done!

scanf

{% hint style="warning" %}
scanf() 最不常用，因为他容易卡住。最好用 getchar()或者fgets()吧。

// input.c -- when to use &
#include <stdio.h>
int main(void)
{
    int age;      // variable
    float assets; // variable
    char pet[30]; // string

    printf("Enter your age, assets, and favorite pet.\n");
    scanf("%d %f", &age, &assets); // use the & here
    scanf("%s", pet);              // no & for char array
    printf("%d $%.2f %s\n", age, assets, pet);

    return 0;
}

// 10 9.9
// a
// 10 $9.90 a

/* skiptwo.c -- skips over first two integers of input */
#include <stdio.h>
int main(void)
{
    int n;
    
    printf("Please enter three integers:\n");
    scanf("%*d %*d %d", &n);
    printf("The last integer was %d\n", n);
    
    return 0;
}

// Please enter three integers:
// 1 2 3
// The last integer was 3

/* scan_str.c -- using scanf() */
#include <stdio.h>
int main(void)
{
    char name1[11], name2[11];
    int count;

    printf("Please enter 2 names.\n");
    count = scanf("%5s %10s", name1, name2);
    printf("I read the %d names %s and %s.\n",
           count, name1, name2);

    return 0;
}

// (base) kimshan@MacBook-Pro output % ./"scan_str"
// Please enter 2 names.
// 123 45
// I read the 2 names 123 and 45.
// (base) kimshan@MacBook-Pro output % ./"scan_str"
// Please enter 2 names.
// 1234567890
// I read the 2 names 12345 and 67890.
// (base) kimshan@MacBook-Pro output % ./"scan_str"
// Please enter 2 names.
// 1234567890 1234567890
// I read the 2 names 12345 and 67890.

getchar, putchar

/* echo_eof.c -- repeats input to end of file */
#include <stdio.h>
int main(void)
{
    int ch;
    
    while ((ch = getchar()) != EOF)
        putchar(ch);
    
    return 0;
}

gets, puts

{% hint style="danger" %}
不要用gets这个函数

#include <stdio.h>
#include <stdlib.h>
int main()
{
    char array1[8];
    fflush(stdin);
    gets(array1); // 1234567
    puts(array1); // 1234567
    char array2[8];
    fflush(stdin);
    gets(array2); // 12345678
    puts(array2); // 12345678
    char array3[8];
    fflush(stdin);
    gets(array3); // 123456789
    puts(array3); // 123456789
    return 0;
}

// (base) kimshan@MacBook-Pro output % ./"a"
// warning: this program uses gets(), which is unsafe.
// 1234567
// 1234567
// 12345678
// 12345678
// 123456789
// 123456789
// (base) kimshan@MacBook-Pro output

/* nono.c -- no! */
#include <stdio.h>
int main(void)
{
    char side_a[] = "Side A";
    char dont[] = {'W', 'O', 'W', '!'};
    char side_b[] = "Side B";

    puts(dont); /* dont is not a string */
    // WOW!Side A

    return 0;
}

fgets, fputs

#include <stdio.h>
#include <stdlib.h>
int main()
{
    char array1[8];
    fflush(stdin);
    fgets(array1, sizeof(array1), stdin); // 1234567
    fputs(array1, stdout); // 1234567
    char array2[8];
    fflush(stdin);
    fgets(array2, sizeof(array2), stdin); // 12345678
    fputs(array2, stdout); // 1234567
    char array3[8];
    fflush(stdin);
    fgets(array3, sizeof(array3), stdin); // 123456789
    fputs(array3, stdout); // 1234567
    return 0;
}

// (base) kimshan@MacBook-Pro output % ./"a"
// 1234567
// 123456712345678
// 1234567123456789
// 1234567%
// (base) kimshan@MacBook-Pro output %

gets_s

{% hint style="danger" %}
很多编译器不支持这个 C11 的新函数！

#include <stdio.h>
#include <stdlib.h>
int main()
{
    char array1[8];
    fflush(stdin);
    gets_s(array1, 8);
    puts(array1);
    char array2[8];
    fflush(stdin);
    gets_s(array2, 8);
    puts(array2);
    char array3[8];
    fflush(stdin);
    gets_s(array3, 8);
    puts(array3);
    return 0;
}

char * s_gets(char * st, int n)
{
    char * ret_val;
    int i = 0;
    
    ret_val = fgets(st, n, stdin);
    if (ret_val)
    {
        while (st[i] != '\n' && st[i] != '\0')
            i++;
        if (st[i] == '\n')
            st[i] = '\0';
        else // must have words[i] == '\0'
            while (getchar() != '\n')
                continue;
    }
    return ret_val;
}

sprintf

/* format.c -- format a string */
#include <stdio.h>
#define MAX 20
char *s_gets(char *st, int n);

int main(void)
{
    char first[MAX];
    char last[MAX];
    char formal[2 * MAX + 10];
    double prize;

    puts("Enter your first name:");
    s_gets(first, MAX);
    puts("Enter your last name:");
    s_gets(last, MAX);
    puts("Enter your prize money:");
    scanf("%lf", &prize);
    sprintf(formal, "%s, %-19s: $%6.2f\n", last, first, prize);
    puts(formal);

    return 0;
}

char *s_gets(char *st, int n)
{
    char *ret_val;
    int i = 0;

    ret_val = fgets(st, n, stdin);
    if (ret_val)
    {
        while (st[i] != '\n' && st[i] != '\0')
            i++;
        if (st[i] == '\n')
            st[i] = '\0';
        else // must have words[i] == '\0'
            while (getchar() != '\n')
                continue;
    }
    return ret_val;
}

// (base) kimshan@MacBook-Pro output % ./"format"
// Enter your first name:
// Charles
// Enter your last name:
// Shan
// Enter your prize money:
// 1000000
// Shan, Charles            : $1000000.00

Reference

[1] https://www.runoob.com/cprogramming/c-function-fflush.html

[2] https://www.pixelbeat.org/programming/gcc/format_specs.html

[3] https://www.gnu.org/software/libc/manual/html_node/Table-of-Output-Conversions.html