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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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