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;

}