main()主函数
每一C 程序都必须有一main()函数, 可以根据自己的爱好把它放在程序的某个地方。有些程序员把它放在最前面, 而另一些程序员把它放在最后面, 无论放在哪个地方, 以下几点说明都是适合的。
1. main() 参数
在Turbo C2.0启动过程中, 传递main()函数三个参数: argc, argv和env。
* argc: 整数, 为传给main()的命令行参数个数。
* argv: 字符串数组。
在DOS 3.X 版本中, argv[0] 为程序运行的全路径名; 对DOS 3.0 以下的版本, argv[0]为空串("") 。
argv[1] 为在DOS命令行中执行程序名后的第一个字符串;
argv[2] 为执行程序名后的第二个字符串;
...
argv[argc]为NULL。
*env: 安符串数组。env[] 的每一个元素都包含ENVVAR=value形式的字符串。其中ENVVAR为环境变量如PATH或87。value 为ENVVAR的对应值如C:\DOS, C:\TURBOC(对于PATH) 或YES(对于87)。
Turbo C2.0启动时总是把这三个参数传递给main()函数, 可以在用户程序中说明(或不说明)它们, 如果说明了部分(或全部)参数, 它们就成为main()子程序的局部变量。
请注意: 一旦想说明这些参数, 则必须按argc, argv, env 的顺序, 如以下的例子:
main()
main(int argc)
main(int argc, char *argv[])
main(int argc, char *argv[], char *env[])
其中第二种情况是合法的, 但不常见, 因为在程序中很少有只用argc, 而不用argv[]的情况。
以下提供一样例程序EXAMPLE.EXE, 演示如何在main()函数中使用三个参数:
/*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]);
}
如果在DOS 提示符下, 按以下方式运行EXAMPLE.EXE:
C:\example first_argument "argument with blanks" 3 4 "last butone" stop!
注意: 可以用双引号括起内含空格的参数, 如本例中的: " argumentwith blanks"和"Last but one")。
结果是这样的:
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 /*视具体设置而定*/
env[2]: PATH=C:\DOS;C:\TC /*视具体设置而定*/
应该提醒的是: 传送main() 函数的命令行参数的最大长度为128 个字符 (包括参数间的空格), 这是由DOS 限制的。
函数名: matherr
功 能: 用户可修改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: 比较两个串s1和s2的前n个字节, 忽略大小写
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 <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: 建立一个目录
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
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拷贝到另一个矩形区域
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();
}
