简易版的printf函数实现

功能说明

（1）使用putchar函数、va可变参完成printf函数基本功能的实现；
（2）函数说明：

实现对下列数据类型的输出，并返回成功输出打印的字符个数：

• 整数（正负）的输出;
• 字符串输出;
• 浮点数（float、double）输出;
• 字符输出;

函数实现

#include <stdio.h>
#include <stdarg.h>
#include <limits.h>
#include <inttypes.h>int myprintf(const char *format, ...) {va_list args;va_start(args, format);int char_count = 0; // 记录写入的字符数量while (*format) {if (*format == '%') {format++;switch (*format) {case 'c': {char c = va_arg(args, int);putchar(c);char_count++;break;}case 'd': {int d = va_arg(args, int);if (d == INT32_MIN) {putchar('-');putchar('2');d = 147483648; char_count += 2;} else if (d < 0) {putchar('-');d = -d;char_count++;}int divisor = 1;while (d / divisor >= 10)divisor *= 10;while (divisor > 0) {putchar(d / divisor + '0');d %= divisor;divisor /= 10;char_count++;}break;}case 's': {char *s = va_arg(args, char *);while (*s) {putchar(*s);s++;char_count++;}break;}case 'l': {format++;switch (*format) {case 'l':format++;if (*format == 'd') {long long ll = va_arg(args, long long);if (ll == LLONG_MIN) {putchar('-');putchar('9');ll = 223372036854775808LL; char_count += 2;} else if (ll < 0) {putchar('-');ll = -ll;char_count++;}unsigned long long divisor = 1;while (ll / divisor >= 10)divisor *= 10;while (divisor > 0) {putchar(ll / divisor + '0');ll %= divisor;divisor /= 10;char_count++;}}break;case 'f': {double lf = va_arg(args, double);int int_part = (int)lf;int fract_part = (int)((lf - int_part) * 1000000); if (lf < 0) {putchar('-');lf = -lf;char_count++;}int divisor = 1;while (int_part / divisor >= 10)divisor *= 10;while (divisor > 0) {putchar(int_part / divisor + '0');int_part %= divisor;divisor /= 10;char_count++;}putchar('.');char_count++;divisor = 100000;while (fract_part / divisor == 0) {putchar('0');divisor /= 10;char_count++;}while (divisor > 0) {putchar(fract_part / divisor + '0');fract_part %= divisor;divisor /= 10;char_count++;}break;}}break;}default:putchar(*format);char_count++;}} else {putchar(*format);char_count++;}format++;}va_end(args);return char_count;
}

测试代码

void test_myprintf_v1() {long long big_number = 12345678901234LL;double pi = 3.141592653589793;myprintf("hello word !\n"); myprintf("LONG LONG: %lld\n", big_number);myprintf("FLOAT: %lf\n", pi);myprintf("INT32_MIN: %d\n", INT32_MIN);myprintf("INT32_MAX: %d\n", INT32_MAX);myprintf("LLONG_MIN: %lld\n", LLONG_MIN);myprintf("%c\n", 'A');return ;
}void test_myprintf_v2() {int ret;//打印字符常量printf("System:\n");ret = printf("hello word\n");printf("成功打印：%d\n", ret);printf("MySelf:\n");ret = myprintf("hello word\n");printf("成功打印：%d\n", ret);putchar(10);  //打印整型变量 int a = INT32_MIN, b = INT32_MAX;printf("System:\n");ret = printf("a = %d, b = %d\n", a, b);printf("成功打印：%d\n", ret);printf("MySelf:\n");ret = myprintf("a = %d, b = %d\n", a, b);printf("成功打印：%d\n", ret);putchar(10);//打印字符char c1 = 'a', c2 ='3';printf("System:\n");ret = printf("c1 = %c, c2 = %c\n", c1, c2);printf("成功打印：%d\n", ret);printf("MySelf:\n");ret = myprintf("c1 = %c, c2 = %c\n", c1, c2);printf("成功打印：%d\n", ret);putchar(10);//打印字符串char s1[150] = "adasdc asd as a", s2[150] ="sdadas asda sdaas";printf("System:\n");ret = printf("s1 = %s, s2 = %s\n", s1, s2);printf("成功打印：%d\n", ret);printf("MySelf:\n");ret = myprintf("s1 = %s, s2 = %s\n", s1, s2);printf("成功打印：%d\n", ret);return ;
}int main() {test_myprintf_v2();return 0;
}

运行效果