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, 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  but one" stop!     注意: 可以用双引号括起内含空格的参数, 如本例中的:   "  argument with 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(); }          

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