C++ 实现 printf 函数
· 阅读需 11 分钟
Front End Engineer
01 实现打印字符串
#include <stdio.h>
int my_printf(const char *frm, ...) {
int cnt = 0;
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
PUTC(frm[i]);
}
return cnt;
}
int main() {
printf("hello world\n");
my_printf("hello world\n");
return 0;
}
02 实现打印变量
int main() {
int a = 123;
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
return 0;
}
#include <stdio.h>
#include <stdarg.h>
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int x = va_arg(arg, int);
while (x) {
PUTC(x % 10 + '0');
x /= 10;
}
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %%\n",a);
return 0;
}
#include <stdio.h>
#include <stdarg.h>
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int x = va_arg(arg, int);
while (x) {
PUTC(x % 10 + '0');
x /= 10;
}
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
return 0;
}
#include <stdio.h>
#include <stdarg.h>
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int temp = va_arg(arg, int);
int x = 0;
while (temp) {
x = x * 10 + temp % 10;
temp /= 10;
}
while (x) {
PUTC(x % 10 + '0');
x /= 10;
}
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
return 0;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
printf("int(1000) = %d\n",1000);
my_printf("int(1000) = %d\n",1000);
return 0;
}
#include <stdio.h>
#include <stdarg.h>
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int temp = va_arg(arg, int);
int x = 0, digit = 0;
while (temp) {
x = x * 10 + temp % 10;
temp /= 10;
digit++;
}
while (digit--) {
PUTC(x % 10 + '0');
x /= 10;
}
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
printf("int(1000) = %d\n",1000);
my_printf("int(1000) = %d\n",1000);
return 0;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
printf("int(1000) = %d\n",1000);
my_printf("int(1000) = %d\n",1000);
printf("int(0) = %d\n",0);
my_printf("int(0) = %d\n",0);
return 0;
}
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int temp = va_arg(arg, int);
int x = 0, digit = 0;
do {
x = x * 10 + temp % 10;
temp /= 10;
digit++;
} while (temp);
while (digit--) {
PUTC(x % 10 + '0');
x /= 10;
}
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
printf("int(1000) = %d\n",1000);
my_printf("int(1000) = %d\n",1000);
printf("int(0) = %d\n",0);
my_printf("int(0) = %d\n",0);
printf("int(-123) = %d\n",-123);
my_printf("int(-123) = %d\n",-123);
return 0;
}
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int temp = va_arg(arg, int);
if (temp < 0) {
PUTC('-'),
temp = -temp;
}
int x = 0, digit = 0;
do {
x = x * 10 + temp % 10;
temp /= 10;
digit++;
} while (temp);
while (digit--) {
PUTC(x % 10 + '0');
x /= 10;
}
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
#include <stdio.h>
#include <stdarg.h>
#include <inttypes.h>
#include <stdint.h>
#include <climits>
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
printf("int(1000) = %d\n",1000);
my_printf("int(1000) = %d\n",1000);
printf("int(0) = %d\n",0);
my_printf("int(0) = %d\n",0);
printf("int(-123) = %d\n",-123);
my_printf("int(-123) = %d\n",-123);
printf("INT_MAX = %d\n", INT_MAX);
my_printf("INT_MAX = %d\n", INT_MAX);
return 0;
}
#include <stdio.h>
#include <stdarg.h>
#include <inttypes.h>
#include <stdint.h>
#include <climits>
int output_num(int num, int digit) {
int cnt = 0;
while (digit--) {
putchar(num % 10 + '0'), ++cnt;
num /= 10;
}
return cnt;
}
int reverse_num(int num, int *temp) {
*temp = 0;
int digit = 0;
do {
*temp = *temp * 10 + num % 10;
num /= 10;
digit++;
} while (num);
return digit;
}
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int temp = va_arg(arg, int);
if (temp < 0) {
PUTC('-'),
temp = -temp;
}
int x1 = temp / 100000, x2 = temp % 100000;
int temp1, temp2;
int digit1 = reverse_num(x1, &temp1);
int digit2 = reverse_num(x2, &temp2);
if (x1) {
digit2 = 5;
} else {
digit1 = 0;
}
cnt += output_num(temp1, digit1);
cnt += output_num(temp2, digit2);
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
printf("int(1000) = %d\n",1000);
my_printf("int(1000) = %d\n",1000);
printf("int(0) = %d\n",0);
my_printf("int(0) = %d\n",0);
printf("int(-123) = %d\n",-123);
my_printf("int(-123) = %d\n",-123);
printf("INT_MAX = %d\n", INT_MAX);
my_printf("INT_MAX = %d\n", INT_MAX);
return 0;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
printf("int(1000) = %d\n",1000);
my_printf("int(1000) = %d\n",1000);
printf("int(0) = %d\n",0);
my_printf("int(0) = %d\n",0);
printf("int(-123) = %d\n",-123);
my_printf("int(-123) = %d\n",-123);
printf("INT_MAX = %d\n", INT_MAX);
my_printf("INT_MAX = %d\n", INT_MAX);
printf("INT_MIN = %d\n", INT_MIN);
my_printf("INT_MIN = %d\n", INT_MIN);
return 0;
}
#include <stdio.h>
#include <stdarg.h>
#include <inttypes.h>
#include <stdint.h>
#include <climits>
int output_num(int num, int digit) {
int cnt = 0;
while (digit--) {
putchar(num % 10 + '0'), ++cnt;
num /= 10;
}
return cnt;
}
int reverse_num(int num, int *temp) {
*temp = 0;
int digit = 0;
do {
*temp = *temp * 10 + num % 10;
num /= 10;
digit++;
} while (num);
return digit;
}
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int temp = va_arg(arg, int);
uint32_t xx = 0;
if (temp < 0) {
PUTC('-'),
xx = -temp;
} else {
xx = temp;
}
int x1 = xx / 100000, x2 = xx % 100000;
int temp1, temp2;
int digit1 = reverse_num(x1, &temp1);
int digit2 = reverse_num(x2, &temp2);
if (x1) {
digit2 = 5;
} else {
digit1 = 0;
}
cnt += output_num(temp1, digit1);
cnt += output_num(temp2, digit2);
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
printf("int(1000) = %d\n",1000);
my_printf("int(1000) = %d\n",1000);
printf("int(0) = %d\n",0);
my_printf("int(0) = %d\n",0);
printf("int(-123) = %d\n",-123);
my_printf("int(-123) = %d\n",-123);
printf("INT_MAX = %d\n", INT_MAX);
my_printf("INT_MAX = %d\n", INT_MAX);
printf("INT_MIN = %d\n", INT_MIN);
my_printf("INT_MIN = %d\n", INT_MIN);
printf("int(100500) = %d\n", 100500);
my_printf("int(100500) = %d\n", 100500);
return 0;
}
#include <stdio.h>
#include <stdarg.h>
#include <inttypes.h>
#include <stdint.h>
#include <climits>
int output_num(int num, int digit) {
int cnt = 0;
while (digit--) {
putchar(num % 10 + '0'), ++cnt;
num /= 10;
}
return cnt;
}
int reverse_num(int num, int *temp) {
*temp = 0;
int digit = 0;
do {
*temp = *temp * 10 + num % 10;
num /= 10;
digit++;
} while (num);
return digit;
}
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int temp = va_arg(arg, int);
uint32_t xx = 0;
if (temp < 0) {
PUTC('-'),
xx = -temp;
} else {
xx = temp;
}
int x1 = xx / 100000, x2 = xx % 100000;
int temp1, temp2;
int digit1 = reverse_num(x1, &temp1);
int digit2 = reverse_num(x2, &temp2);
int digit3 = 0;
if (x1) {
digit3 = 5 - digit2;
} else {
digit1 = 0;
}
cnt += output_num(temp1, digit1);
cnt += output_num(0, digit3);
cnt += output_num(temp2, digit2);
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
03 效果
#include <stdio.h>
#include <stdarg.h>
#include <inttypes.h>
#include <stdint.h>
#include <climits>
int output_num(int num, int digit) {
int cnt = 0;
while (digit--) {
putchar(num % 10 + '0'), ++cnt;
num /= 10;
}
return cnt;
}
int reverse_num(int num, int *temp) {
*temp = 0;
int digit = 0;
do {
*temp = *temp * 10 + num % 10;
num /= 10;
digit++;
} while (num);
return digit;
}
int my_printf(const char *frm, ...) {
int cnt = 0;
va_list arg;
va_start(arg, frm);
#define PUTC(a) putchar(a), ++cnt
for (int i = 0; frm[i]; i ++) {
// putchar(frm[i]),++cnt;
switch (frm[i]) {
case '%' : {
switch (frm[++i]) {
case '%' : PUTC(frm[i]); break;
case 'd' : {
int temp = va_arg(arg, int);
uint32_t xx = 0;
if (temp < 0) {
PUTC('-'),
xx = -temp;
} else {
xx = temp;
}
int x1 = xx / 100000, x2 = xx % 100000;
int temp1, temp2;
int digit1 = reverse_num(x1, &temp1);
int digit2 = reverse_num(x2, &temp2);
int digit3 = 0;
if (x1) {
digit3 = 5 - digit2;
} else {
digit1 = 0;
}
cnt += output_num(temp1, digit1);
cnt += output_num(0, digit3);
cnt += output_num(temp2, digit2);
} break;
case 'f' : {
} break;
}
} break;
default: PUTC(frm[i]); break;
}
}
return cnt;
}
int main() {
int a = 123;
printf("hello world\n");
my_printf("hello world\n");
printf("int(123) = %d\n",a);
my_printf("int(123) = %d\n",a);
printf("int(1000) = %d\n",1000);
my_printf("int(1000) = %d\n",1000);
printf("int(0) = %d\n",0);
my_printf("int(0) = %d\n",0);
printf("int(-123) = %d\n",-123);
my_printf("int(-123) = %d\n",-123);
printf("INT_MAX = %d\n", INT_MAX);
my_printf("INT_MAX = %d\n", INT_MAX);
printf("INT_MIN = %d\n", INT_MIN);
my_printf("INT_MIN = %d\n", INT_MIN);
printf("int(100500) = %d\n", 100500);
my_printf("int(100500) = %d\n", 100500);
int n;
while (~scanf("%d", &n)) {
printf(" has %d digits !\n", printf("%d", n));
my_printf(" has %d digits !\n", my_printf("%d", n));
}
return 0;
}
