常用字符，整形，浮点型相互装换函…

首先就是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+4,5);

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

int main()

{

char str[] = "wangyucao1989";

char newstr[6];

//memcpy(newstr,str+4,5);

strncpy(newstr,str+4,5);

newstr[5] = '\0';

printf("%s\n",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

<< 左移运算

运用这些基本的运算，我们可以解决acm所需的各种运算,给Bit赋1，赋0，给他的值取反，还有好多段操作。如下：

功能 | 示例 | 位运算

-----------------+---------------------+--------------------

去掉最后一位 | (101101->10110) | x >> 1

在最后加一个0 | (101101->1011010) | x < < 1

在最后加一个1 | (101101->1011011) | x < < 1+1

把最后一位变成1 | (101100->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 < < (k-1))

把右数第k位变成0 | (101101->101001,k=3) | x & ~ (1 < < (k-1))

右数第k位取反 | (101001->101101,k=3) | x ^ (1 < < (k-1))

取末三位 | (1101101->101) | x & 7

取末k位 | (1101101->1101,k=5) | x & ((1 < < k)-1)

取右数第k位 | (1101101->1,k=4) | x >> (k-1) & 1

把末k位变成1 | (101001->101111,k=4) | x | (1 < < k-1)

末k位取反 | (101001->100110,k=4) | x ^ (1 < < k-1)

把右边连续的1变成0 | (100101111->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

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

int main(void)

{

int number = -1234;

printf("number: %d absolute value: %d\n", 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

int main(void)

{

float f;

char *str = "12345.67";

f = atof(str);

printf("string = %s float = %f\n", 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

int main(void)

{

int n;

char *str = "12345.67";

n = atoi(str);

printf("string = %s integer = %d\n", 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

int main(void)

{

long l;

char *str = "98765432";

l = atol(lstr);

printf("string = %s integer = %ld\n", 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

#define NELEMS(arr) (sizeof(arr) / sizeof(arr[0]))

int numarray[] = {123, 145, 512, 627, 800, 933};

int numeric (const int *p1, const int *p2)

{

return(*p1 - *p2);

}

int lookup(int key)

{

int *itemptr;

itemptr = bsearch (&key, numarray, NELEMS(numarray),

sizeof(int), (int(*)(const void *,const void *))numeric);

return (itemptr != NULL);

}

int main(void)

{

if (lookup(512))

printf("512 is in the table.\n");

else

printf("512 isn't 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

int main(void)

{

float number = -1234.0;

printf("number: %f absolute value: %f\n",

number, fabs(number));

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

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 = %d\n", string, dec, sign);

value = -123.45;

ndig= 15;

string = ecvt(value,ndig,&dec,&sign);

printf("string = %s dec = %d sign = %d\n",

string, dec, sign);

value = 0.6789e5;

ndig = 5;

string = ecvt(value,ndig,&dec,&sign);

printf("string = %s dec = %d\

sign = %d\n", 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 *buf);

程序例:

#include

int main(void)

{

char str[25];

double num;

int sig = 5;

num = 9.876;

gcvt(num, sig, str);

printf("string = %s\n", str);

num = -123.4567;

gcvt(num, sig, str);

printf("string = %s\n", str);

num = 0.678e5;

gcvt(num, sig, str);

printf("string = %s\n", 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

int main(void)

{

int number = 12345;

char string[25];

itoa(number, string, 10);

printf("integer = %d string = %s\n", 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

int main(void)

{

long result;

long x = -12345678L;

result= labs(x);

printf("number: %ld abs value: %ld\n",

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

int main(void)

{

char src[] = "******************************";

char dest[] = "abcdefghijlkmnopqrstuvwxyz0123456709";

char *ptr;

printf("destination before memcpy: %s\n", dest);

ptr = memcpy(dest, src, strlen(src));

if (ptr)

printf("destination after memcpy: %s\n", dest);

else

printf("memcpy failed\n");

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

int main(void)

{

char buffer[] = "Hello world\n";

printf("Buffer before memset: %s\n", buffer);

memset(buffer, '*', strlen(buffer) - 1);

printf("Buffer after memset: %s\n", 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

int main(void)

{

double x = 2.0, y = 3.0;

printf("%lf raised to %lf is %lf\n", x, y, pow(x, y));

return 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

int sort_function( const void *a, const void *b);

char list[5][4] = { "cat", "car", "cab", "cap", "can" };

int main(void)

{

int x;

qsort((void *)list, 5, sizeof(list[0]), sort_function);

for (x = 0; x < 5; x++)

printf("%s\n", list[x]);

return 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

int main(void)

{

double x = 4.0, result;

result = sqrt(x);

printf("The square root of %lf is %lf\n", 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 *format[,argument,...]);

程序例:

#include

int main(void)

{

char label[20];

char name[20];

int entries = 0;

int loop, age;

double salary;

struct Entry_struct

{

char name[20];

int age;

float salary;

} entry[20];

printf("\n\nPlease enter a label for the chart: ");

scanf(" s", label);

fflush(stdin);

printf("How many entries will there be? (less than 20) ");

scanf("%d", &entries);

fflush(stdin);

for (loop=0;loop

{

printf("Entry %d\n", loop);

printf(" Name : ");

scanf("%[A-Za-z]", entry[loop].name);

fflush(stdin);

printf(" Age : ");

scanf("%d", &entry[loop].age);

fflush(stdin);

printf(" Salary : ");

scanf("%f", &entry[loop].salary);

fflush(stdin);

}

printf("\nPlease enter your name, age and salary\n");

scanf(" s %d %lf", name, &age, &salary);

printf("\n\nTable %s\n",label);

printf("Compiled by %s age %d $.2lf\n", name, age, salary);

printf("-----------------------------------------------------\n");

for (loop=0;loop

printf("M | %-20s | ] | .2lf\n",

loop + 1,

entry[loop].name,

entry[loop].age,

entry[loop].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 *source);

程序例:

#include

int main(void)

{

char string[10];

char *str1 = "abcdefghi";

stpcpy(string, str1);

printf("%s\n", 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

int main(void)

{

char destination[25];

char *blank = " ", *c = "C++", *Borland = "Borland";

strcpy(destination, Borland);

strcat(destination, blank);

strcat(destination, c);

printf("%s\n", 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

int main(void)

{

char string[15];

char *ptr, c = 'r';

strcpy(string, "This is a string");

ptr = strchr(string, c);

if (ptr)

printf("The character %c is at position: %d\n", c, ptr-string);

else

printf("The character was not found\n");

return 0;

}

函数名: strcmp

功能: 串比较

用法: int strcmp(char *str1, char *str2);

程序例:

#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 1\n");

else

printf("buffer 2 is less than buffer 1\n");

ptr = strcmp(buf2, buf3);

if (ptr > 0)

printf("buffer 2 is greater than buffer 3\n");

else

printf("buffer 2 is less than buffer 3\n");

return 0;

}

函数名: strcpy

功能: 串拷贝用法: char *strcpy(char *str1, char *str2);

程序例:

#include

int main(void)

{

char string[10];

char *str1 = "abcdefghi";

strcpy(string, str1);

printf("%s\n", string);

return 0;

}

函数名: strrev

功能: 串倒转用法: char *strrev(char *str);

程序例:

#include

int main(void)

{

char *forward = "string";

printf("Before strrev(): %s\n", forward);

strrev(forward);

printf("After strrev(): %s\n", 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

int main(void)

{

char string[10] = "123456789";

char symbol = 'c';

printf("Before strset(): %s\n", string);

strset(string, symbol);

printf("After strset(): %s\n", 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

int main(void)

{

char *str1 = "Borland International", *str2 = "nation", *ptr;

ptr = strstr(str1, str2);

printf("The substring is: %s\n", 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

int main(void)

{

char input[80], *endptr;

double value;

printf("Enter a floating point number:");

gets(input);

value = strtod(input, &endptr);

printf("The string is %s the number is %lf\n", 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

int main(void)

{

char *string = "87654321", *endptr;

long lnumber;

lnumber = strtol(string, &endptr, 10);

printf("string = %s long = %ld\n", string, lnumber);

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

int main(void)

{

char *string = "abcdefghijklmnopqrstuvwxyz", *ptr;

ptr = strupr(string);

printf("%s\n", 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

int main(void)

{

int length, i;

char *string = "THIS IS A STRING";

length = strlen(string);

for (i=0; i

{

string[i] = tolower(string[i]);

}

printf("%s\n",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

int main(void)

{

int length, i;

char *string = "this is a string";

length = strlen(string);

for (i=0; i

{

string[i] = toupper(string[i]);

}

printf("%s\n",string);

return 0;

}