main()主函數
每一C 程序都必須有一main()函數, 可以根據自己的愛好把它放在程序的某
個地方。有些程序員把它放在最前面, 而另一些程序員把它放在最面, 無論放
在哪個地方, 以下幾點說明都是適合的。
1. main() 參數
在Turbo C2.0啟動過程中, 傳遞main()函數三個參數: argc, argv和env。
* argc: 整數, 為傳給main()的命令行參數個數。
* argv: 字符串數組。
在DOS 3.X 版本中, argv[0] 為程序運行的全路徑名; 對DOS 3.0
以下的版本, argv[0]為空串("") 。
argv[1] 為在DOS命令行中執行程序名的第一個字符串;
argv[2] 為執行程序名的第二個字符串;
...
argv[argc]為NULL。
*env: 安符串數組。env[] 的每一個元素都包含ENVVAR=value形式的字符
串。其中ENVVAR為環境變量如PATH或87。value 為ENVVAR的對應值如C:\DOS, C:
\TURBOC(對PATH) 或YES(對87)。
Turbo C2.0啟動時總是把這三個參數傳遞給main()函數, 可以在用戶程序中
說明(或不說明)它們, 如果說明了部分(或全部)參數, 它們就成為main()子程序
的局部變量。
請注意: 一旦想說明這些參數, 則必須按argc, argv, env 的順序, 如以下
的例子:
main()
main(int argc)
main(int argc, char *argv[])
main(int argc, char *argv[], char *env[])
其中第二種情況是合法的, 但不常見, 因為在程序中很少有只用argc, 而不
用argv[]的情況。
以下提供一樣例程序EXAMPLE.EXE, 演示如何在main()函數中使用三個參數:
/*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]);
}
如果在DOS 提示符下, 按以下方式運行EXAMPLE.EXE:
C:\example first_argument "argument with blanks" 3 4 "last but
one" stop!
注意: 可以用雙引號括起內含空格的參數, 如本例中的: " argument
with blanks"和"Last but one")。
結果是這樣的:
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 /*視具體設置而定*/
env[2]: PATH=C:\DOS;C:\TC /*視具體設置而定*/
應該提醒的是: 傳送main() 函數的命令行參數的最大長度為128 個字符 (包
括參數間的空格), 這是由DOS 限制的。
函數名: matherr
功 能: 用戶可修改的數學錯誤處理程序
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;
}
函數名: memccpy
功 能: 從源source中拷貝n個字節到目標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;
}
函數名: malloc
功 能: 內存分配函數
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;
}
函數名: memchr
功 能: 在數組的前n個字節中搜索字符
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;
}
函數名: memcpy
功 能: 從源source中拷貝n個字節到目標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;
}
函數名: memicmp
功 能: 比較兩個串s1和s2的前n個字節, 忽略大小寫
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;
}
函數名: memmove
功 能: 移動一塊字節
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;
}
函數名: memset
功 能: 設置s中的所有字節為ch, s數組的大小由n給定
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;
}
函數名: mkdir
功 能: 建立一個目錄
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;
}
函數名: mktemp
功 能: 建立唯一的文件名
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;
}
函數名: MK_FP
功 能: 設置一個遠指針
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;
}
函數名: modf
功 能: 把數分為指數和尾數
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;
}
函數名: movedata
功 能: 拷貝字節
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);
}
函數名: moverel
功 能: 將當前位置(CP)移動一相對距離
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;
}
函數名: movetext
功 能: 將屏幕文本從一個矩形區域拷貝到另一個矩形區域
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;
}
函數名: moveto
功 能: 將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;
}
函數名: movemem
功 能: 移動一塊字節
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;
}
函數名: normvideo
功 能: 選擇正常亮度字符
用 法: void normvideo(void);
程序例:
#include <conio.h>
int main(void)
{
normvideo();
cprintf("NORMAL Intensity Text\r\n");
return 0;
}
函數名: nosound
功 能: 關閉PC揚聲器
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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