c语言函数---M

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                      main()主函数
    每一C 程序都必须有一main()函数, 能够依据自己的爱好把它放在程序的某 

个地方。有些程序猿把它放在最前面, 而还有一些程序猿把它放在最后面, 不管放

在哪个地方, 下面几点说明都是适合的。

    1. main() 參数
    在Turbo C2.0启动过程中, 传递main()函数三个參数: argc, argv和env。

* argc:  整数, 为传给main()的命令行參数个数。

* argv:  字符串数组。
              在DOS 3.X 版本号中, argv[0] 为程序运行的全路径名; 对DOS 3.0
              下面的版本号, argv[0]为空串("") 。

argv[1] 为在DOS命令行中运行程序名后的第一个字符串;
              argv[2] 为运行程序名后的第二个字符串;
              ...
              argv[argc]为NULL。
     *env:  安符串数组。

env[] 的每个元素都包括ENVVAR=value形式的字符 

串。

当中ENVVAR为环境变量如PATH或87。value 为ENVVAR的相应值如C:\DOS, C:

\TURBOC(对于PATH) 或YES(对于87)。

Turbo C2.0启动时总是把这三个參数传递给main()函数, 能够在用户程序中 

说明(或不说明)它们, 假设说明了部分(或所有)參数, 它们就成为main()子程序

的局部变量。

    请注意: 一旦想说明这些參数, 则必须按argc, argv, env 的顺序, 例如以下面 

的样例:

     main()
     main(int argc)
     main(int argc, char *argv[])
     main(int argc, char *argv[], char *env[]) 

当中另外一种情况是合法的, 但不常见, 由于在程序中非常少有仅仅用argc, 而不

用argv[]的情况。

    下面提供一例子程序EXAMPLE.EXE,  演示怎样在main()函数中使用三个參数:
     /*program name EXAMPLE.EXE*/
     #include <stdio.h>
     #include <stdlib.h>
     main(int argc, char *argv[], char *env[])
     {
          int i;
          printf("These are the %d  command- line  arguments passed  to
                  main:\n\n", argc);
          for(i=0; i<=argc; i++)
            printf("argv[%d]:%s\n", i, argv[i]);
          printf("\nThe environment string(s)on this system are:\n\n");
          for(i=0; env[i]!=NULL; i++)
               printf(" env[%d]:%s\n", i, env[i]);
     }
    假设在DOS 提示符下, 按下面方式执行EXAMPLE.EXE:
    C:\example first_argument "argument with blanks"  3  4  "last  but
one" stop!
    注意: 能够用双引號括起内含空格的參数, 如本例中的:   "  argument
with blanks"和"Last but one")。

结果是这种:
     The value of argc is 7
     These are the 7 command-linearguments passed to main:
     argv[0]:C:\TURBO\EXAMPLE.EXE
     argv[1]:first_argument
     argv[2]:argument with blanks
     argv[3]:3
     argv[4]:4
     argv[5]:last but one
     argv[6]:stop!
     argv[7]:(NULL)
     The environment string(s) on this system are:
     env[0]: COMSPEC=C:\COMMAND.COM
     env[1]: PROMPT=$P$G            /*视详细设置而定*/
     env[2]: PATH=C:\DOS;C:\TC      /*视详细设置而定*/ 

应该提醒的是: 传送main() 函数的命令行參数的最大长度为128 个字符 (包

括參数间的空格), 这是由DOS 限制的。

函数名: matherr

功 能: 用户可改动的数学错误处理程序

用 法: int matherr(struct exception *e);

程序例:

/* This is a user-defined matherr function that prevents
   any error messages from being printed. */
#include<math.h>
int matherr(struct exception *a)
{
   return 1;
} 

函数名: memccpy

功 能: 从源source中拷贝n个字节到目标destin中

用 法: void *memccpy(void *destin, void *source, unsigned char ch,

       unsigned n); 

程序例:

#include <string.h>
#include <stdio.h>
int main(void)
{
   char *src = "This is the source string";
   char dest[50];
   char *ptr;
   ptr = memccpy(dest, src, 'c', strlen(src));
   if (ptr)
   {
      *ptr = '\0';
      printf("The character was found:  %s\n", dest);
   }
   else
      printf("The character wasn't found\n");
   return 0;
} 

函数名: malloc

功 能: 内存分配函数

用 法: void *malloc(unsigned size);

程序例:

#include <stdio.h>
#include <string.h>
#include <alloc.h>
#include <process.h>
int main(void)
{
   char *str;
   /* allocate memory for string */
   /* This will generate an error when compiling */
   /* with C++, use the new operator instead. */
   if ((str = malloc(10)) == NULL)
   {
      printf("Not enough memory to allocate buffer\n");
      exit(1);  /* terminate program if out of memory */
   }
   /* copy "Hello" into string */
   strcpy(str, "Hello");
   /* display string */
   printf("String is %s\n", str);
   /* free memory */
   free(str);
   return 0;
} 

函数名: memchr

功 能: 在数组的前n个字节中搜索字符

用 法: void *memchr(void *s, char ch, unsigned n);

程序例:

#include <string.h>
#include <stdio.h>
int main(void)
{
   char str[17];
   char *ptr;
   strcpy(str, "This is a string");
   ptr = memchr(str, 'r', strlen(str));
   if (ptr)
      printf("The character 'r' is at position: %d\n", ptr - str);
   else
      printf("The character was not found\n");
   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 <stdio.h>
#include <string.h>
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: memicmp

功 能: 比較两个串s1和s2的前n个字节, 忽略大写和小写

用 法: int memicmp(void *s1, void *s2, unsigned n);

程序例:

#include <stdio.h>
#include <string.h>
int main(void)
{
   char *buf1 = "ABCDE123";
   char *buf2 = "abcde456";
   int stat;
   stat = memicmp(buf1, buf2, 5);
   printf("The strings to position 5 are ");
   if (stat)
      printf("not ");
   printf("the same\n");
   return 0;
} 

函数名: memmove

功 能: 移动一块字节

用 法: void *memmove(void *destin, void *source, unsigned n);

程序例:

#include <string.h>
#include <stdio.h>
int main(void)
{
  char *dest = "abcdefghijklmnopqrstuvwxyz0123456789";
  char *src = "******************************";
  printf("destination prior to memmove: %s\n", dest);
  memmove(dest, src, 26);
  printf("destination after memmove:    %s\n", dest);
  return 0;
} 

函数名: memset

功 能: 设置s中的全部字节为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 <string.h>
#include <stdio.h>
#include <mem.h>
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: mkdir

功 能: 建立一个文件夹

用 法: int mkdir(char *pathname);

程序例:

#include <stdio.h>
#include <conio.h>
#include <process.h>
#include <dir.h>
int main(void)
{
  int status;
   clrscr();
   status = mkdir("asdfjklm");
   (!status) ? (printf("Directory created\n")) :
               (printf("Unable to create directory\n"));
   getch();
   system("dir");
   getch();
   status = rmdir("asdfjklm");
   (!status) ? (printf("Directory deleted\n")) :
  (perror("Unable to delete directory"));
   return 0;
} 

函数名: mktemp

功 能: 建立唯一的文件名称

用 法: char *mktemp(char *template);

程序例:

#include <dir.h>
#include <stdio.h>
int main(void)
{
   /* fname defines the template for the
     temporary file.  */
   char *fname = "TXXXXXX", *ptr;
   ptr = mktemp(fname);
   printf("%s\n",ptr);
   return 0;
} 

函数名: MK_FP

功 能: 设置一个远指针

用 法: void far *MK_FP(unsigned seg, unsigned off);

程序例:

#include <dos.h>
#include <graphics.h>
int main(void)
{
   int gd, gm, i;
   unsigned int far *screen;
   detectgraph(&gd, &gm);
   if (gd == HERCMONO)
       screen = MK_FP(0xB000, 0);
   else
       screen = MK_FP(0xB800, 0);
   for (i=0; i<26; i++)
      screen[i] = 0x0700 + ('a' + i);
   return 0;
} 

函数名: modf

功 能: 把数分为指数和尾数

用 法: double modf(double value, double *iptr);

程序例:

#include <math.h>
#include <stdio.h>
int main(void)
{
   double fraction, integer;
   double number = 100000.567;
   fraction = modf(number, &integer);
   printf("The whole and fractional parts of %lf are %lf and %lf\n",
          number, integer, fraction);
   return 0;
} 

函数名: movedata

功 能: 拷贝字节

用 法: void movedata(int segsrc, int offsrc, int segdest,

  int offdest, unsigned numbytes); 

程序例:

#include <mem.h>
#define MONO_BASE 0xB000
/* saves the contents of the monochrome screen in buffer */
void save_mono_screen(char near *buffer)
{
   movedata(MONO_BASE, 0, _DS, (unsigned)buffer, 80*25*2);
}
int main(void)
{
   char buf[80*25*2];
   save_mono_screen(buf);
} 

函数名: moverel

功 能: 将当前位置(CP)移动一相对距离

用 法: void far moverel(int dx, int dy);

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;
   char msg[80];
   /* 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 */
   }
   /* move the C.P. to location (20, 30) */
   moveto(20, 30);
   /* plot a pixel at the C.P. */
   putpixel(getx(), gety(), getmaxcolor());
   /* create and output a message at (20, 30) */
   sprintf(msg, " (%d, %d)", getx(), gety());
   outtextxy(20, 30, msg);
   /* move to a point a relative distance */
   /* away from the current value of C.P. */
   moverel(100, 100);
   /* plot a pixel at the C.P. */
   putpixel(getx(), gety(), getmaxcolor());
   /* create and output a message at C.P. */
   sprintf(msg, " (%d, %d)", getx(), gety());
   outtext(msg);
   /* clean up */
   getch();
   closegraph();
   return 0;
} 

函数名: movetext

功 能: 将屏幕文本从一个矩形区域复制到还有一个矩形区域

用 法: int movetext(int left, int top, int right, int bottom,

  int newleft, int newtop); 

程序例:

#include <conio.h>
#include <string.h>
int main(void)
{
   char *str = "This is a test string";
   clrscr();
   cputs(str);
   getch();
   movetext(1, 1, strlen(str), 2, 10, 10);
   getch();
   return 0;
} 

函数名: moveto

功 能: 将CP移到(x, y)

用 法: void far moveto(int x, int y);

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;
   char msg[80];
   /* 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 */
   }
   /* move the C.P. to location (20, 30) */
   moveto(20, 30);
   /* plot a pixel at the C.P. */
   putpixel(getx(), gety(), getmaxcolor());
   /* create and output a message at (20, 30) */
   sprintf(msg, " (%d, %d)", getx(), gety());
   outtextxy(20, 30, msg);
   /* move to (100, 100) */
   moveto(100, 100);
   /* plot a pixel at the C.P. */
   putpixel(getx(), gety(), getmaxcolor());
   /* create and output a message at C.P. */
   sprintf(msg, " (%d, %d)", getx(), gety());
   outtext(msg);
   /* clean up */
   getch();
   closegraph();
   return 0;
} 

函数名: movemem

功 能: 移动一块字节

用 法: void movemem(void *source, void *destin, unsigned len);

程序例:

#include <mem.h>
#include <alloc.h>
#include <stdio.h>
#include <string.h>
int main(void)
{
   char *source = "Borland International";
   char *destination;
   int length;
   length = strlen(source);
   destination = malloc(length + 1);
   movmem(source,destination,length);
   printf("%s\n",destination);
   return 0;
} 

函数名: normvideo

功 能: 选择正常亮度字符

用 法: void normvideo(void);

程序例:

#include <conio.h>
int main(void)
{
   normvideo();
   cprintf("NORMAL Intensity Text\r\n");
   return 0;
} 

函数名: nosound

功 能: 关闭PC扬声器

用 法: void nosound(void);

程序例:

/* Emits a 7-Hz tone for 10 seconds.
     True story: 7 Hz is the resonant frequency of a chicken's skull cavity.
     This was determined empirically in Australia, where a new factory
     generating 7-Hz tones was located too close to a chicken ranch:
     When the factory started up, all the chickens died.
     Your PC may not be able to emit a 7-Hz tone.
*/
int main(void)
{
   sound(7);
   delay(10000);
   nosound();
} 

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