The C Programming Language (second edition) 实践代码（置于此以作备份）

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include<time.h>

#define myPrint(expr) printf(#expr " =%d\n",expr);
//2-3
int htoi(char *s)
{
    int n=0;
    while(*s!=‘\0‘)
    {
        if (*s==‘x‘ || *s==‘X‘)
        {
            n=0;
        }
        else if (‘0‘<=*s && *s<=‘9‘)
        {
            n=n*16+(*s-‘0‘);
        }
        else if (‘a‘<=*s && *s<=‘z‘)
        {
            n=n*16+(*s-‘a‘+10);
        }
        else if (‘A‘<=*s && *s<=‘Z‘)
        {
            n=n*16+(*s-‘A‘+10);
        }
        s++;
    }
    return n;
}
void swap(int &x,int &y)
{
    x^=y;
    y^=x;
    x^=y;
}//x,y不能是数组的同一个元素

unsigned getbits(unsigned x,int p,int n)
{//从右向左数从0起，取从p开始向右的n个位，的值
    return (x>>(p+1-n)) & ~(~0<<n);
}
//2-6
unsigned setbits(unsigned x,int p,int n,unsigned y)
{//把x从右起从0起向右的n位置为y最右n位
    y&=~(~0<<n);//得到y最右n位
    y<<=(p+1-n);//最右n位左移到与x中间n位对应的位置上

    y|=x & (~(~0<<n));//使y最右n位与x最右n位一样
    x>>=(p+1);
    x<<=(p+1);//得到x里p位置左边的部分
    y|=x;
    return y;
}
//2-7
unsigned invert(unsigned x,int p,int n)
{
    //return setbits(x,p,n,~getbits(x,p,n));
    return x ^(~(~0<<n)<<(p-n+1));
}
//2-8
unsigned rightrot(unsigned x,int n)
{//0^a=a,1^a=~a
    return ((~(~0<<n) & x)<<(sizeof(unsigned)*8-n)) ^ (x>>n);
}

//递归，将一个整数作为字符串打印
int isNegtive=1;
void printd(int n)
{        if(n<0 && isNegtive)
{
    putchar(‘-‘);
    isNegtive=0;
}
if (n/10)
{
    printd(n/10);
}
putchar((n%10<0)?(-n%10+‘0‘):(n%10+‘0‘));
}

//快排的另一种写法
void quickSort(int data[],int left,int right)
{
    int i,last;
    if(left>=right)
        return;
    
    //partition
    last=left;
    for (i=left+1;i<=right;i++)
    {
        if ((data[i]<data[left]) && (++last!=i))
        {
            data[last]^=data[i];
            data[i]^=data[last];
            data[last]^=data[i];
        }
    }
    if(last!=left)
    {
        data[left]^=data[last];
        data[last]^=data[left];
        data[left]^=data[last];
    }
    
    //recursive
    quickSort(data,left,last-1);
    quickSort(data,last+1,right);
}
int binSearch(int data[],int n,int num)
{
    int low,high,mid;
    low=0;
    high=n-1;
    while (low<=high)
    {
        mid=(low+high)/2;
        if (num==data[mid])
            return mid;
        else if (num>data[mid])
            low=mid+1;
        else
            high=mid-1;
    }
    return -1;
}
int main()
{
    int c=1,d=2;
    swap(c,d);
    printf("c:%d d:%d\n",c,d);
    printf("%u\n",getbits(-2,2,3));
    printf("%u\n",setbits(25,4,3,1));
    printf("%u\n",invert(32,4,3));
    printf("%x\n",rightrot(0xff00ff,4));

    extern void mytest();
    mytest();

    int testdata[]={4,3,2,5,6,9,8};
    quickSort(testdata,0,6);
    for (c=0;c<7;c++)
    {
        printf("%d ",testdata[c]);
    }

    printf("\na" " b%d\n",3);//前面的两个字符串将被连接起来
    myPrint(c);
    return 0;
}
void mytest()
{
    extern int num;
    printf("\n%d\n",num);
}
int num=2;

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include<time.h>
#include <string.h>
#include <limits.h>
//2-3
int htoi(char *s)
{
    int n=0;
    while(*s!=‘\0‘)
    {
        if (*s==‘x‘ || *s==‘X‘)
        {
            n=0;
        }
        else if (‘0‘<=*s && *s<=‘9‘)
        {
            n=n*16+(*s-‘0‘);
        }
        else if (‘a‘<=*s && *s<=‘z‘)
        {
            n=n*16+(*s-‘a‘+10);
        }
        else if (‘A‘<=*s && *s<=‘Z‘)
        {
            n=n*16+(*s-‘A‘+10);
        }
        s++;
    }
    return n;
}
unsigned getbits(unsigned x,int p,int n)
{//从右向左数从0起，取从p开始向右的n个位，的值
    return (x>>(p+1-n)) & ~(~0<<n);
}
//2-6
unsigned setbits(unsigned x,int p,int n,unsigned y)
{//把x从右起从0起向右的n位置为y最右n位
    y&=~(~0<<n);//得到y最右n位
    y<<=(p+1-n);//最右n位左移到与x中间n位对应的位置上
    
    y|=x & (~(~0<<n));//使y最右n位与x最右n位一样
    x>>=(p+1);
    x<<=(p+1);//得到x里p位置左边的部分
    y|=x;
    return y;
}
//2-7
unsigned invert(unsigned x,int p,int n)
{
    //return setbits(x,p,n,~getbits(x,p,n));
    return x ^(~(~0<<n)<<(p-n+1));
}
//2-8
unsigned rightrot(unsigned x,int n)
{//0^a=a,1^a=~a
    return ((~(~0<<n) & x)<<(sizeof(unsigned)*8-n)) ^ (x>>n);
}
//2-9
int bitcount(unsigned x)
{//x的二进制形式中1的个数
    int n=0;
    while(x!=0)
    {
        //         if (x & 1)
        //         {
        //             n++;
        //         }//method1
        {
            x&=(x-1);
            n++;
        }//method2
        x>>=1;
    }
    return n;
}
char * reverse(char s[])
{
    int i,j;
    for (i=0,j=strlen(s)-1;i<j;i++,j--)
    {
        s[i]^=s[j];
        s[j]^=s[i];
        s[i]^=s[j];
    }
    return s;
}
//3-4
char * itoa(int num)
{//num需在int范围内
    int i=0;
    bool isNegative=num<0?true:false;
    char s[100];//数的位数，包括可能的负号
    if (isNegative)
    {
        do 
        {
            s[i++]=-(num%10)+‘0‘;
            num/=10;
        } while(num!=0);
        s[i++]=‘-‘;
    }
    else
    {
        do 
        {
            s[i++]=num%10+‘0‘;
            num/=10;
        } while(num!=0);
    }
    s[i]=‘\0‘;
    reverse(s);
    return s;
}
int main()
{
    char s[]="abcde423546g";
    printf("getbits: %u\n",getbits(-2,2,3));
    printf("setbits: %u\n",setbits(25,4,3,1));
    printf("invert:  %u\n",invert(32,4,3));
    printf("rightrot:%x\n",rightrot(0xff00ff,4));
    printf("bitcount:%d\n",bitcount(131));
    printf("reverse: %s\n",reverse(s));
    printf("itoa:    %s\n",itoa(INT_MIN));
    printf("itoa:    %s\n",itoa(INT_MAX));
    return 0;
}

#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>

void printIntArgs(int arg1, ...) /* 输出所有int类型的参数，直到-1结束 */
{//变长参数表处理
    va_list ap;
    int i;
    va_start(ap, arg1);
    for (i = arg1; i != -1; i = va_arg(ap, int))
        printf("%d ", i);
    va_end(ap);
    putchar(‘\n‘);
}
void myPrintf(int a,char *format,...)
{//变长参数表处理
    char *p;
    
    va_list ap;//参数指针
    
    va_start(ap,a);//初始化ap，指向某个有名参数
    printf("%s\n",va_arg(ap,int));//再次调用后，ap指向最后一个有名参数。
    //在处理格式串前，必须将ap指向最后一个有名参数
    
    for (p=format;*p;p++)
    {
        if (*p!=‘%‘)
        {
            putchar(*p);
            continue;
        }
        switch(*++p)
        {
        case ‘d‘:
            printf("%d",va_arg(ap,int));
            break;
        case ‘f‘:
            printf("%f",va_arg(ap,double));
            break;
        case ‘s‘:
            printf("%s",va_arg(ap,char *));
            break;
        case ‘c‘:
            printf("%c",va_arg(ap,char));
            break;
        }
    }
    va_end(ap);
}



void myScanf(char *format,...)
{//变长参数表处理
    char *p;
    
    va_list ap;//参数指针
    
    //在处理格式串前，必须将ap指向最后一个有名参数
    va_start(ap,format);
    
    for (p=format;*p;p++)
    {
        if (*p!=‘%‘)
        {
            continue;
        }
        ++p;
        switch(*p)
        {//myScanf实参如&a传的是地址，所以里面参数值就是地址值，因此调用scanf时只要能按指针4字节得到其值即可
        case ‘d‘:
            scanf("%d",va_arg(ap,void *));
            break;
        case ‘f‘:
            scanf("%f",va_arg(ap, void *));
            break;
        case ‘s‘:
            scanf("%s",va_arg(ap,void *));
            break;
        case ‘c‘:
            scanf("%c",va_arg(ap,void *));
            break;
        }
    }
    va_end(ap);
}


void scanfFormatTest()
{//scanf格式特性示例
    char s[20];
    sscanf("123456abcd","%[1-4a-z]",s);
    printf("%s\n",s);//1234
    s[0]=‘\0‘;
    
    sscanf("123456abcd","%[14az]",s);
    printf("%s\n",s);//1
    s[0]=‘\0‘;
    
    sscanf("123456abcd","%[^3-4]",s);
    printf("%s\n",s);//12
    s[0]=‘\0‘;
    
    sscanf("a123456abcd","%[3-4]",s);
    printf("%s\n",s);//空，虽然串中有34但不是从首字符起的
    s[0]=‘\0‘;
    
    sscanf("123456abcd","%3[0-9a-z]",s);
    printf("%s\n",s);//123，限定最多读取3个字符
    s[0]=‘\0‘;
    
    sscanf("a123456,abcd","%*c%s",s);
    printf("%s\n",s);//123456,abcd，*  表示跳过此数据不读入. (也就是不把此数据读入参数中)
    s[0]=‘\0‘;
    
    sscanf("iios/12DDWDFF@122","%*[^/]/%[^@]",s);
    printf("%s\n",s);//12DDWDFF，综合使用，某种程度上可以充当正则使用
    s[0]=‘\0‘;
}


struct stu
{
    char name[10];
    int num;
    int age;
    char addr[15];
}boya[2],boyb[2],*pp,*qq;
void freadFwriteTest()
{//fread、fwrite示例
    FILE *fp;
    char ch;
    int i;
    pp=boya;
    qq=boyb;
    if((fp=fopen("stu_list.txt","wb+"))==NULL)
    {
        printf("Cannot open file strike any key exit!");
        getchar();
    }
    printf("input data");
    for(i=0;i<2;i++,pp++)
        scanf("%s%d%d%s",pp->name,&pp->num,&pp->age,pp->addr);
    pp=boya;
    fwrite(pp,sizeof(struct stu),2,fp);
    rewind(fp);
    fread(qq,sizeof(struct stu),2,fp);
    printf("name number age addr");
    for(i=0;i<2;i++,qq++)
        printf("%s %5d%7d%s",qq->name,qq->num,qq->age,qq->addr);
    fclose(fp);
    getchar();
}


void StderrExitTest(int argc,char *argv[])
{
    FILE *fp;
    void filecopy(FILE *,FILE *);
    char *prog=argv[0];
    if(argc==1)
        filecopy(stdin,stdout);
    else
    {
        while (--argc>0)
        {
            if ((fp=fopen(*++argv,"r"))==NULL)
            {
                fprintf(stderr,"%s: can‘t open %s\n",prog,*argv);
                //exit(1);
            }
            else
            {
                filecopy(fp,stdout);
                fclose(fp);
            }
        }
    }
    if (ferror(stdout))
    {
        fprintf(stderr,"%s: error writing stdout\n",prog);
        exit(2);
    }
    exit(0);
}
void filecopy(FILE *ifp,FILE *ofp)
{
    int c;
    while ((c=getc(ifp))!=EOF)
    {
        putc(c,ofp);
    }
}


void ungetcTest()
{
    char str[100];
    FILE *fp=fopen("file2.txt","r+");//文件file2.txt的内容：jklmn
    
    putc(getc(fp),stdout);//j
    putc(getc(fp),stdout);//k
    
    ungetc (‘e‘, fp);
    ungetc (‘f‘, fp);
    ungetc (‘g‘, fp);
    
    //fscanf(fp,"%s",str);
    //printf("**%s**\n",str);//**felmn**
    
    putc(getc(fp),stdout);//f
    putc(getc(fp),stdout);//e
    putc(getc(fp),stdout);//l
    
    ungetc (‘a‘, fp);
    ungetc (‘b‘, fp);
    ungetc (‘c‘, fp);
    
    printf ("%c", getc(fp));//c
    printf ("%c", getc(fp));//b
    printf ("%c", getc(fp));//a
    printf ("%c", getc(fp));//m
    printf ("%c", getc(fp));//n
}
void mallocMemsetTest()
{
    int * p=NULL;
    
    p=(int *)malloc(3*sizeof(int));//malloc不能自动初始化
    if(NULL==p){
        printf("Can‘t get memory!\n");
        return -1;
    }
    
    printf("%d\n\n",*p);//未初始化的不定乱值-842150451
    
    memset(p,1,2*sizeof(int));     //用c++的函数memset初始化前两个数
    
    printf("%d\n",*p);//初始化值16843009
    printf("%d\n",p[1]==0x01010101);//1，说明每个字节被0x01代替
    printf("%d\n",p[2]);//未初始化乱值-842150451
    
    *(p+2)=2;
    
    printf("%d\n\n",p[2]);//2
    
    free(p);//动态分配者在程序结束前必须释放，否则内存泄露
    printf("%d\n",*p);;//乱值-572662307。free后指针仍指向原来指向的地方，为野指针
    
    return 0;
}

void callocTest()
{
    int * p=NULL;
    int i=0;
    int SIZE=10;
    //为p从堆上分配SIZE个int型空间
    p=(int *)calloc(SIZE,sizeof(int));
    //p=(int *)malloc(SIZE*sizeof(int));与上句功能一样，只不过没有自动初始化

    if(NULL==p){
        printf("Error in calloc.\n");
        return -1;
    }
    //输出各个空间的值
    for(i=0;i<SIZE;i++)
        printf("p[%d]=%d\n",i,p[i]);

    //为p指向的SIZE个int型空间赋值
    for(i=0;i<SIZE;i++)
        p[i]=i;
    
    //输出各个空间的值
    for(i=0;i<SIZE;i++)
        printf("p[%d]=%d\n",i,p[i]);
    
    free(p);
    p=NULL;
    return 0;
}


//模拟c语言中的带缓冲的getchar(), syscalls.h
int myGetchar(void)
{
    static char buf[100];
    static char *bufp=buf;
    static int n=0;
    if (n==0)
    {
        n=read(0,buf,sizeof(buf));
        bufp=buf;
    }
    return (n-->0)?(unsigned char)*bufp++:EOF;
}

int intAverage(int x,int y)
{//x,y和为负时会出错，如-4、3结果会得到-1，正确为0
    return ( (x & y) + ( (x^y) >>1 ));
}
int intOpposite(int x)
{//-x=~x+1=~(x+`)
    return (~x+1);//~(X+1)
}
int intAbs(int x)
{//无分支取绝对值
    int y=x>>(8*sizeof(x)-1);
    return (x^y)-y;//(x+y)^y
}


//递归实现进制转换
void decimalTranslate(int n,int desBase){
    if(desBase>16 || desBase<2){
        printf("error:desBase should be between[2,16]\n");
        exit(0);
    }
    if(n){
        decimalTranslate(n/desBase,desBase);
        printf("%x",n%desBase);
    }
}
int main(int argc,char *argv[])
{
    char a;
    char b[20]="helloworld";
    int c;
    float d;
    //变长参数表处理
    //printIntArgs(2,1,3,4,-1);
    //myPrintf(3," char:%c\n int:%d\n double%f\n string:%s\n",‘ab‘,12,12.2,"hello world" " good");
    //myScanf("%c%s%d%f",&a,b,&c,&d);
    //printf("%c %s %d %f\n",a,b,c,d);
    
    //scanf格式特性示例
    //scanfFormatTest();
    
    //fread fwrite示例
    //freadFwriteTest();
    
    //stdrr exit示例
    //StderrExitTest(argc,argv);
    
    //ungetc示例
    //ungetcTest();

    //存储管理函数示例
    //mallocMemsetTest();
    //callocTest();

    //putchar(myGetchar());

    //rename("fi.txt","file");
    printf("%+d %+d\n",-10,10);//加号，输出正负号
    printf("% d % d % d\n",-10,+10,10);//一个空格，若数的第一个字符为符号位，则代替该空格
    printf("%x\n",013);
    printf("hello%d  %n",10,&c);printf("%d\n",c);//%n
    return 0;
    
}