程序设计竞赛——C++常用库函数.pdf

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1、转自：http:/ memcpy 表头文件:#include 定义函数:void*memcpy(void*dest,const void*src,size_t n)函数说明:memcpy()用来拷贝 src 所指的内存内容前n 个字节到 dest 所指的内存地址上。与 strcpy()不同的是,memcpy()会完整的复制 n 个字节,不会因为遇到字符串结束 0 而结束返回值:返回指向 dest 的指针附加说明:指针 src 和 dest 所指的内存区域不可重叠例如：你需要复制串 str=“wangyucao1989”中的“yucao”，那么可以这么写：memcpy(newstr,str+4,

2、5);除了 memcpy之外，string 还提供了 strncpy 函数：函数名称:strncpy 函数原型:char*strncpy(char*dest,const char*src，int count)函数功能:将字符串 src 中的 count个字符拷贝到字符串dest 中去函数返回:指向 dest 的指针参数说明:dest-目的字符串，src-源字符串，count-拷贝的字符个数所属文档:还是上面的例子，这个程序可以这样写：#include#include int main()char str=wangyucao1989;char newstr6;/memcpy(newstr,str

3、+4,5);strncpy(newstr,str+4,5);newstr5=0;printf(%sn,newstr);return 0;=位运算：运算方法有六种：&与运算|或运算 异或运算 非运算(求补)右移运算10110)|x 1 在最后加一个 0|(101101-1011010)|x 1011011)|x 101101)|x|1 把最后一位变成 0|(101101-101100)|x|1-1 最后一位取反|(101101-101100)|x 1 把右数第 k 位变成 1|(101001-101101,k=3)|x|(1 101001,k=3)|x&(1 101101,k=3)|x (1 1

4、01)|x&7 取末 k 位|(1101101-1101,k=5)|x&(1 1,k=4)|x (k-1)&1 把末 k 位变成 1|(101001-101111,k=4)|x|(1 100110,k=4)|x (1 100100000)|x&(x+1)把右起第一个 0 变成 1|(100101111-100111111)|x|(x+1)把右边连续的 0 变成 1|(11011000-11011111)|x|(x-1)取右边连续的 1|(100101111-1111)|(x (x+1)1 去掉右起第一个 1 的左边|(100101000-1000)|x&(x (x-1)判断奇数(x&1)=1

5、判断偶数(x&1)=0 取右边第一个 1 所在位置 x&-x=类型转换：函数名:abs 功能:求整数的绝对值用法:int abs(int i);程序例:#include#include int main(void)int number=-1234;printf(number:%d absolute value:%dn,number,abs(number);return 0;函数名:atof 功能:把字符串转换成浮点数用法:double atof(const char*nptr);程序例:#include#include int main(void)float f;char*str=12345.

6、67;f=atof(str);printf(string=%s float=%fn,str,f);return 0;函数名:atoi 功能:把字符串转换成长整型数用法:int atoi(const char*nptr);程序例:#include#include int main(void)int n;char*str=12345.67;n=atoi(str);printf(string=%s integer=%dn,str,n);return 0;函数名:atol 功能:把字符串转换成长整型数用法:long atol(const char*nptr);程序例:#include#include

7、int main(void)long l;char*str=98765432;l=atol(lstr);printf(string=%s integer=%ldn,str,l);return(0);=其他函数：函数名:bsearch 功能:二分法搜索用法:void*bsearch(const void*key,const void*base,size_t*nelem,size_t width,int(*fcmp)(const void*,const*);程序例:#include#include#define NELEMS(arr)(sizeof(arr)/sizeof(arr0)int num

8、array=123,145,512,627,800,933;int numeric(const int*p1,const int*p2)return(*p1-*p2);int lookup(int key)int*itemptr;/*The cast of(int(*)(const void*,const void*)is needed to avoid a type mismatch error at compile time*/itemptr=bsearch(&key,numarray,NELEMS(numarray),sizeof(int),(int(*)(const void*,con

9、st void*)numeric);return(itemptr!=NULL);int main(void)if(lookup(512)printf(512 is in the table.n);else printf(512 isnt in the table.n);return 0;函数名:fabs 功能:返回浮点数的绝对值用法:double fabs(double x);程序例:#include#include int main(void)float number=-1234.0;printf(number:%f absolute value:%fn,number,fabs(number

10、);return 0;函数名:fcvt 功能:把一个浮点数转换为字符串用法:char*fcvt(double value,int ndigit,int*decpt,int*sign);程序例:#include#include#include int main(void)char*string;double value;int dec,sign;int ndig=10;clrscr();value=9.876;string=ecvt(value,ndig,&dec,&sign);printf(string=%s dec=%d sign=%dn,string,dec,sign);value=-12

11、3.45;ndig=15;string=ecvt(value,ndig,&dec,&sign);printf(string=%s dec=%d sign=%dn,string,dec,sign);value=0.6789e5;/*scientific notation*/ndig=5;string=ecvt(value,ndig,&dec,&sign);printf(string=%s dec=%d sign=%dn,string,dec,sign);return 0;函数名:gcvt 功能:把浮点数转换成字符串用法:char*gcvt(double value,int ndigit,char

12、*buf);程序例:#include#include int main(void)char str25;double num;int sig=5;/*significant digits*/*a regular number*/num=9.876;gcvt(num,sig,str);printf(string=%sn,str);/*a negative number*/num=-123.4567;gcvt(num,sig,str);printf(string=%sn,str);/*scientific notation*/num=0.678e5;gcvt(num,sig,str);printf

13、(string=%sn,str);return(0);函数名:itoa 功能:把一整数转换为字符串用法:char*itoa(int value,char*string,int radix);程序例:#include#include int main(void)int number=12345;char string25;itoa(number,string,10);printf(integer=%d string=%sn,number,string);return 0;函数名:labs 功能:取长整型绝对值用法:long labs(long n);程序例:#include#include in

14、t main(void)long result;long x=-12345678L;result=labs(x);printf(number:%ld abs value:%ldn,x,result);return 0;函数名:memcpy 功能:从源 source 中拷贝 n 个字节到目标 destin 中用法:void*memcpy(void*destin,void*source,unsigned n);程序例:#include#include int main(void)char src=*;char dest=abcdefghijlkmnopqrstuvwxyz0123456709;ch

15、ar*ptr;printf(destination before memcpy:%sn,dest);ptr=memcpy(dest,src,strlen(src);if(ptr)printf(destination after memcpy:%sn,dest);else printf(memcpy failedn);return 0;函数名:memset 功能:设置 s中的所有字节为ch,s 数组的大小由 n 给定用法:void*memset(void*s,char ch,unsigned n);程序例:#include#include#include int main(void)char b

16、uffer=Hello worldn;printf(Buffer before memset:%sn,buffer);memset(buffer,*,strlen(buffer)-1);printf(Buffer after memset:%sn,buffer);return 0;函数名:pow 功能:指数函数(x 的 y 次方)用法:double pow(double x,double y);程序例:#include#include int main(void)double x=2.0,y=3.0;printf(%lf raised to%lf is%lfn,x,y,pow(x,y);ret

17、urn 0;函数名:qsort 功能:使用快速排序例程进行排序用法:void qsort(void*base,int nelem,int width,int(*fcmp)();程序例:#include#include#include int sort_function(const void*a,const void*b);char list54=cat,car,cab,cap,can;int main(void)int x;qsort(void*)list,5,sizeof(list0),sort_function);for(x=0;x 5;x+)printf(%sn,listx);retur

18、n 0;int sort_function(const void*a,const void*b)return(strcmp(a,b);函数名:sqrt 功能:计算平方根用法:double sqrt(double x);程序例:#include#include int main(void)double x=4.0,result;result=sqrt(x);printf(The square root of%lf is%lfn,x,result);return 0;=字符串函数：函数名:sscanf 功能:执行从字符串中的格式化输入用法:int sscanf(char*string,char*f

19、ormat,argument,.);程序例:#include#include int main(void)char label20;char name20;int entries=0;int loop,age;double salary;struct Entry_struct char name20;int age;float salary;entry20;/*Input a label as a string of characters restricting to 20 characters*/printf(nnPlease enter a label for the chart:);sc

20、anf(%20s,label);fflush(stdin);/*flush the input stream in case of bad input*/*Input number of entries as an integer*/printf(How many entries will there be?(less than 20);scanf(%d,&entries);fflush(stdin);/*flush the input stream in case of bad input*/*input a name restricting input to only letters up

21、per or lower case*/for(loop=0;loopentries;+loop)printf(Entry%dn,loop);printf(Name:);scanf(%A-Za-z,entryloop.name);fflush(stdin);/*flush the input stream in case of bad input*/*input an age as an integer*/printf(Age:);scanf(%d,&entryloop.age);fflush(stdin);/*flush the input stream in case of bad inpu

22、t*/*input a salary as a float*/printf(Salary:);scanf(%f,&entryloop.salary);fflush(stdin);/*flush the input stream in case of bad input*/*Input a name,age and salary as a string,integer,and double*/printf(nPlease enter your name,age and salaryn);scanf(%20s%d%lf,name,&age,&salary);/*Print out the data

23、 that was input*/printf(nnTable%sn,label);printf(Compiled by%s age%d$%15.2lfn,name,age,salary);printf(-n);for(loop=0;loopentries;+loop)printf(%4d|%-20s|%5d|%15.2lfn,loop+1,entryloop.name,entryloop.age,entryloop.salary);printf(-n);return 0;函数名:stpcpy 功能:拷贝一个字符串到另一个用法:char*stpcpy(char*destin,char*sour

24、ce);程序例:#include#include int main(void)char string10;char*str1=abcdefghi;stpcpy(string,str1);printf(%sn,string);return 0;函数名:strcat 功能:字符串拼接函数用法:char*strcat(char*destin,char*source);程序例:#include#include int main(void)char destination25;char*blank=,*c=C+,*Borland=Borland;strcpy(destination,Borland);s

25、trcat(destination,blank);strcat(destination,c);printf(%sn,destination);return 0;函数名:strchr 功能:在一个串中查找给定字符的第一个匹配之处 用法:char*strchr(char*str,char c);程序例:#include#include int main(void)char string15;char*ptr,c=r;strcpy(string,This is a string);ptr=strchr(string,c);if(ptr)printf(The character%c is at pos

26、ition:%dn,c,ptr-string);else printf(The character was not foundn);return 0;函数名:strcmp 功能:串比较用法:int strcmp(char*str1,char*str2);程序例:#include#include int main(void)char*buf1=aaa,*buf2=bbb,*buf3=ccc;int ptr;ptr=strcmp(buf2,buf1);if(ptr 0)printf(buffer 2 is greater than buffer 1n);else printf(buffer 2 i

27、s less than buffer 1n);ptr=strcmp(buf2,buf3);if(ptr 0)printf(buffer 2 is greater than buffer 3n);else printf(buffer 2 is less than buffer 3n);return 0;函数名:strcpy 功能:串拷贝用法:char*strcpy(char*str1,char*str2);程序例:#include#include int main(void)char string10;char*str1=abcdefghi;strcpy(string,str1);printf(

28、%sn,string);return 0;函数名:strrev 功能:串倒转用法:char*strrev(char*str);程序例:#include#include int main(void)char*forward=string;printf(Before strrev():%sn,forward);strrev(forward);printf(After strrev():%sn,forward);return 0;函数名:strset 功能:将一个串中的所有字符都设为指定字符用法:char*strset(char*str,char c);程序例:#include#include in

29、t main(void)char string10=123456789;char symbol=c;printf(Before strset():%sn,string);strset(string,symbol);printf(After strset():%sn,string);return 0;函数名:strstr 功能:在串中查找指定字符串的第一次出现用法:char*strstr(char*str1,char*str2);程序例:#include#include int main(void)char*str1=Borland International,*str2=nation,*ptr

30、;ptr=strstr(str1,str2);printf(The substring is:%sn,ptr);return 0;函数名:strtod 功能:将字符串转换为double型值用法:double strtod(char*str,char*endptr);程序例:#include#include int main(void)char input80,*endptr;double value;printf(Enter a floating point number:);gets(input);value=strtod(input,&endptr);printf(The string i

31、s%s the number is%lfn,input,value);return 0;函数名:strtol 功能:将串转换为长整数用法:long strtol(char*str,char*endptr,int base);程序例:#include#include int main(void)char*string=87654321,*endptr;long lnumber;/*strtol converts string to long integer*/lnumber=strtol(string,&endptr,10);printf(string=%s long=%ldn,string,l

32、number);return 0;函数名:strupr 功能:将串中的小写字母转换为大写字母用法:char*strupr(char*str);程序例:#include#include int main(void)char*string=abcdefghijklmnopqrstuvwxyz,*ptr;/*converts string to upper case characters*/ptr=strupr(string);printf(%sn,ptr);return 0;函数名:tolower 功能:把字符转换成小写字母用法:int tolower(int c);程序例:#include#in

33、clude#include int main(void)int length,i;char*string=THIS IS A STRING;length=strlen(string);for(i=0;ilength;i+)stringi=tolower(stringi);printf(%sn,string);return 0;函数名:toupper 功能:把字符转换成大写字母用法:int toupper(int c);程序例:#include#include#include int main(void)int length,i;char*string=this is a string;length=strlen(string);for(i=0;ilength;i+)stringi=toupper(stringi);printf(%sn,string);return 0;