CH7-1 输入输出

输入输出库 <stdio.h> <string.h> <ctype.h>

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7.1  标准输入输出

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
//<和>表示在标准库位置寻找，UNIX下一般在/usr/include中
//stdio.h中 int c = getchar(); putchar(c); printf(); EOF
//ctype.h中 tolower(c); toupper(c);
//stdlib.h中 EXIT_SUCCESS
int main(int argc, char** argv) {
                printf("Please input the 1st string end with Ctrl+D:\n");
                int c;                                                        
                while((c = getchar()) != EOF)        //EOF表示结束，Ctrl+D，//int getchar(void)
                                putchar(tolower(c));  //tolower函数包含在ctype.h头文件中

                printf("Please input the 2nd string end with Ctrl+D:\n");
                int ch;
                while((ch = getchar()) != EOF)
                                putchar(toupper(ch)); //toupper函数包含在ctype.h头文件中

                printf("EOF's value is: %d\n", EOF); //EOF定义在stdio.h中，值为-1
                return (EXIT_SUCCESS);  //EXIT_SUCCESS 一般为0
}

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7.2  格式化输出 printf  sprintf

#include <stdio.h>
/* int printf(char *format, arg1, arg2, ...);  //返回打印字符个数
* %[-][width].[precision][conversion]
* %% 当打印%时，须%%         printf("Hello World! %%\n");
* - 表示左对齐，无表示右对齐
* width 至少宽度。若其值不够长，则左端或右端用空格补齐；若超过，则全部显示。
                                printf("%2d\n", 123456); 结果为12345
                                printf("%10d\n", 123456);结果为        123456
* precision        (1)若string类型，则最大打印的字符数,若不足，不补
                                        printf("%.2s\n", "123456789");结果为12
                                (2)若浮点型，则小数点后的精度(缺省为6)，若不足用0补齐
                                        printf("%.2f\n", 123.456); 结果为123.45
                                        printf("%.5f\n", 123.456); 结果为123.4500
                                (3)若是整型，为最小显示长度
                                        printf("%.2d\n", 1);    结果为01
*/
int main(int argc, char** argv) {
        printf("%d\n", -123);     //-123
        printf("%o\n", 123);        //173
        printf("%x\n", 123);        //7b
        printf("%u\n", 123);        //123
        
        printf("%c\n", 123);        //{
        
        printf("%s\n", "123");     //123

        printf("%f\n", 123.456); //123.456000 (缺省为6)
        printf("%e\n", 123.456); //1.234560E+02（缺省为6）
        printf("%g\n", 123.456); //123.456
        return 0;
}

 

#include <stdio.h>
// int sprintf(char *string, char *format, arg1, arg2, ...);
//string的长度必须能容下format的长度，包括'\0'.
int main(int argc, char** argv) {
        char str[20];
        sprintf(str, "Score is: %d \n", 34);
        printf("%s\n", str);
        return 0;
}

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7.3 函数参数个数可变举例

#include <stdio.h>
#include <stdarg.h> //va_start,va_arg,va_end
//例子：函数参数个数可变
void minprintf(char *format, ...){ //注意：...表示参数的个数和类型可变
        va_list argumentPointer; //变量list
        char *p;
        int intVal;
        double doubleVal;
        char *strVal;

        va_start(argumentPointer, format); //argumentPointer指向第一个无名参数

        for(p = format; *p; p++){ //遍历format中的每一个字符
                if(*p != '%'){             //如果不是%，则直接putchar打印出来
                        putchar(*p);
                        continue;
                }
                switch(*++p){             //如果是%，则判断其下一个字符
                        case 'd':
                                intVal = va_arg(argumentPointer, int); //va_arg以int型取一个参数，并将argumentPointer指向下一个参数
                                printf("%d", intVal);
                                break;
                        case 'f':
                                doubleVal = va_arg(argumentPointer, double);
                                printf("%f", doubleVal);
                                break;
                        case 's':
                                for(strVal = va_arg(argumentPointer, char*); *strVal; strVal++)
                                        putchar(*strVal);
                                break;
                        default:
                                putchar(*p);
                                break;
                }
        }
        va_end(argumentPointer);
}

int main(int argc, char** argv) {
        minprintf("My name is: %s, age is: %d, height is: %f\n", "amao", 30, 165.5);
        minprintf("My name is: %s, age is: %d\n", "stone", 22);
        return 0;
}

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7.4  格式化输出 scanf

#include <stdio.h>
/*
* int scanf(char *format, arg1，...) //返回成功保存的参数个数
* 以format将标准输入保存到{参数指向的地址}中，arg1等参数必须为地址指针
*    
* int sscanf(char *string, char *format, arg1, arg2, ...);
* 从string中读取数据
*/
/*    
* d,u,i,o,x的前面可以加 h 表示short,l(ell)表示long
*/
void scanfInteger(){
        int n;
        scanf("%d", &n);     //按照十进制将整数读入，并存在n的地址空间中
        printf("%d\n", n);

        scanf("%u", &n);     //按照十进制将无符号整数读入
        printf("%d\n", n);

        scanf("%i", &n);     //按照八进制(0开头)或者十六(0x开头)进制读入
        printf("%d\n", n); //若输入017，输出15 //若输入0xf，输出15

        scanf("%o", &n);     //按照八进制(0开头可有可无)读入
        printf("%d\n", n); //若输入17，输出15 //若输入017，输出15

        scanf("%x", &n);     //按十六进制(0x开头可有可无)读入
        printf("%d\n", n); //若输入0xf，输出15 //若输入f，输出15
}
/*
* %c 读取下一个字符，注意有可能是空字符，若要录入第一个非空字符,请用%1s
* %c 相当于 getchar()
*/
int scanfCharString(){
        char ch;
        char str[20];        
        scanf("%c, %s", &ch, str); //输入a,amao
        printf("%c %s\n", ch, str);//输出a amao
}
/*
* f,e,g以不同的格式录入float，lf表示录入的double而非float
* 输入：12.34 12.34 12.34 12345.6789
* 输出：12.340000 1.234000e+01 12.34 12345.678900
*/
int scanfFloat(){
        float    f1, f2, f3;
        double d1;
        scanf("%f %e %g %lf", &f1, &f2, &f3, &d1);    
        printf("%f %e %g %f\n", f1, f2, f3, d1);
}

void sscanfTest(){
        int n, num;
        float f;
        num = sscanf("123 12.34", "%d %f", &n, &f);
        printf("n = %d f = %f num = %d \n", n, f, num);
}

int main1(int argc, char** argv) {
        scanfInteger();
        scanfCharString();
        scanfFloat();
        sscanfTest();                
        return 0;
}

例子：

#include <stdio.h>

void acc(){
        float i, sum = 0;
        while(scanf("%f", &i) == 1)
                printf("%.2f\n", sum += i);
}

int getline(char *line, int max){ //fgets从文件中读一行
        if(fgets(line, max, stdin) == NULL) //stdin标准输入
                return 0;
        else
                return strlen(line);    //strlen返回字符串line的长度
}

void time(){
        int day, month, year;
        char monthName[20];
        
        char line[20];    //思考：为什么char *line不行？？？
        while(getline(line, sizeof(line)) > 0){    
                if(sscanf(line, "%d %s %d", &day, monthName, &year) == 3)
                        printf("valid: %s\n", line);    //输入31 sep 2001
                else if(sscanf(line, "%d/%d/%d", &month, &day, &year) == 3)
                        printf("valid: %s\n", line);    //输入9/31/2001 mm/dd/yy
                else printf("invalid: %s\n", line);
        }
}

int main(int argc, char** argv) {
        acc();
        time();
        return 0;
}

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注意：

#include <stdio.h>

int main(int argc, char** argv) {
        char str1[20], *str2;    //str1是一段空间的头地址
        scanf("%s", str1);
        
        //scanf("%s", str2); //错误，原因是str2只是声明为一个char型指针，其还未开辟空间，故不能接收字符串
        //printf("%s %s\n", str1, str2);

        str2 = str1; //str2指向了str1开始的空间
        scanf("%s", str2);
        printf("%s %s\n", str1, str2);    
}