C语言库函数(C类字母)

C语言库函数(C类字母)


函数名: cabs
功 能: 计算复数的绝对值
用 法: double cabs(struct complex z);
程序例:
#include <stdio.h>
#include <math.h>

int main(void)
{
struct complex z;
double val;

z.x = 2.0;
z.y = 1.0;
val = cabs(z);

printf("The absolute value of %.2lfi %.2lfj is %.2lf", z.x, z.y, val);
return 0;
}




函数名: calloc
功 能: 分配主存储器
用 法: void *calloc(size_t nelem, size_t elsize);
程序例:

#include <stdio.h>
#include <alloc.h>

int main(void)
{
char *str = NULL;

/* allocate memory for string */
str = calloc(10, sizeof(char));

/* copy "Hello" into string */
strcpy(str, "Hello");

/* display string */
printf("String is %s\n", str);

/* free memory */
free(str);

return 0;
}




函数名: ceil
功 能: 向上舍入
用 法: double ceil(double x);
程序例:

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

int main(void)
{
double number = 123.54;
double down, up;

down = floor(number);
up = ceil(number);

printf("original number %5.2lf\n", number);
printf("number rounded down %5.2lf\n", down);
printf("number rounded up %5.2lf\n", up);

return 0;
}




函数名: cgets
功 能: 从控制台读字符串
用 法: char *cgets(char *str);
程序例:

#include <stdio.h>
#include <conio.h>

int main(void)
{
char buffer[83];
char *p;

/* There's space for 80 characters plus the NULL terminator */
buffer[0] = 81;

printf("Input some chars:");
p = cgets(buffer);
printf("\ncgets read %d characters: \"%s\"\n", buffer[1], p);
printf("The returned pointer is %p, buffer[0] is at %p\n", p, &buffer);

/* Leave room for 5 characters plus the NULL terminator */
buffer[0] = 6;

printf("Input some chars:");
p = cgets(buffer);
printf("\ncgets read %d characters: \"%s\"\n", buffer[1], p);
printf("The returned pointer is %p, buffer[0] is at %p\n", p, &buffer);
return 0;
}




函数名: chdir
功 能: 改变工作目录
用 法: int chdir(const char *path);
程序例:

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

char old_dir[MAXDIR];
char new_dir[MAXDIR];

int main(void)
{
if (getcurdir(0, old_dir))
{
perror("getcurdir()");
exit(1);
}
printf("Current directory is: \\%s\n", old_dir);

if (chdir("\\"))
{
perror("chdir()");
exit(1);
}

if (getcurdir(0, new_dir))
{
perror("getcurdir()");
exit(1);
}
printf("Current directory is now: \\%s\n", new_dir);

printf("\nChanging back to orignal directory: \\%s\n", old_dir);
if (chdir(old_dir))
{
perror("chdir()");
exit(1);
}

return 0;
}



函数名: _chmod, chmod
功 能: 改变文件的访问方式
用 法: int chmod(const char *filename, int permiss);
程序例:

#include <sys\stat.h>
#include <stdio.h>
#include <io.h>

void make_read_only(char *filename);

int main(void)
{
make_read_only("NOTEXIST.FIL");
make_read_only("MYFILE.FIL");
return 0;
}

void make_read_only(char *filename)
{
int stat;

stat = chmod(filename, S_IREAD);
if (stat)
printf("Couldn't make %s read-only\n", filename);
else
printf("Made %s read-only\n", filename);
}




函数名: chsize
功 能: 改变文件大小
用 法: int chsize(int handle, long size);
程序例:

#include <string.h>
#include <fcntl.h>
#include <io.h>

int main(void)
{
int handle;
char buf[11] = "0123456789";

/* create text file containing 10 bytes */
handle = open("DUMMY.FIL", O_CREAT);
write(handle, buf, strlen(buf));

/* truncate the file to 5 bytes in size */
chsize(handle, 5);

/* close the file */
close(handle);
return 0;
}



函数名: circle
功 能: 在给定半径以(x, y)为圆心画圆
用 法: void far circle(int x, int y, int radius);
程序例:

#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>

int main(void)
{
/* request auto detection */
int gdriver = DETECT, gmode, errorcode;
int midx, midy;
int radius = 100;

/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();
if (errorcode != grOk) /* an error occurred */
{
printf("Graphics error: %s\n", grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1); /* terminate with an error code */
}

midx = getmaxx() / 2;

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