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<HTML><HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=gb2312"> <META NAME="Author" CONTENT="wdg"> <META NAME="GENERATOR" CONTENT="Mozilla/4.03 [en] (Win95; I) [Netscape]"> <TITLE>fm</TITLE></HEAD><BODY> main()主函数<P> 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<BR>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<BR>在哪个地方, 以下几点说明都是适合的。<BR> 1. main() 参数<BR> 在Turbo C2.0启动过程中, 传递main()函数三个参数:argc, argv和env。<BR> * argc: 整数, 为传给main()的命令行参数个数。<BR> * argv: 字符串数组。<BR> 在DOS 3.X 版本中, argv[0] 为程序运行的全路径名; 对DOS 3.0<BR> 以下的版本, argv[0]为空串("") 。<BR> argv[1] 为在DOS命令行中执行程序名后的第一个字符串;<BR> argv[2] 为执行程序名后的第二个字符串;<BR> ...<BR> argv[argc]为NULL。<BR> *env: 安符串数组。env[] 的每一个元素都包含ENVVAR=value形式的字符<BR>串。其中ENVVAR为环境变量如PATH或87。value 为ENVVAR的对应值如C:\DOS,C:<BR>\TURBOC(对于PATH) 或YES(对于87)。<BR> 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<BR>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<BR>的局部变量。<BR> 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<BR>的例子:<BR> main()<BR> main(int argc)<BR> main(int argc, char *argv[])<BR> main(int argc, char *argv[], char *env[])<BR> 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<BR>用argv[]的情况。<BR> 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:<BR> /*program name EXAMPLE.EXE*/<BR> #include <stdio.h><BR> #include <stdlib.h><BR> main(int argc, char *argv[], char *env[])<BR> {<BR> int i;<BR> printf("Theseare the %d command- line arguments passed to<BR> main:\n\n", argc);<BR> for(i=0; i<=argc;i++)<BR> printf("argv[%d]:%s\n", i, argv[i]);<BR> printf("\nTheenvironment string(s)on this system are:\n\n");<BR> for(i=0; env[i]!=NULL;i++)<BR> printf(" env[%d]:%s\n", i, env[i]);<BR> }<BR> 如果在DOS 提示符下, 按以下方式运行EXAMPLE.EXE:<BR> C:\example first_argument "argument with blanks" 3 4 "last but<BR>one" stop!<BR> 注意: 可以用双引号括起内含空格的参数, 如本例中的: " argument<BR>with blanks"和"Last but one")。<BR> 结果是这样的:<BR> The value of argc is 7<BR> These are the 7 command-linearguments passedto main:<BR> argv[0]:C:\TURBO\EXAMPLE.EXE<BR> argv[1]:first_argument<BR> argv[2]:argument with blanks<BR> argv[3]:3<BR> argv[4]:4<BR> argv[5]:last but one<BR> argv[6]:stop!<BR> argv[7]:(NULL)<BR> The environment string(s) on this system are:<BR> env[0]: COMSPEC=C:\COMMAND.COM<BR> env[1]: PROMPT=$P$G /*视具体设置而定*/<BR> env[2]: PATH=C:\DOS;C:\TC /*视具体设置而定*/<BR> <BR> 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<BR>括参数间的空格), 这是由DOS 限制的。<BR> <P>函数名: matherr<BR>功 能: 用户可修改的数学错误处理程序<BR>用 法: int matherr(struct exception *e);<BR>程序例:<P>/* This is a user-defined matherr function that prevents<BR> any error messages from being printed. */<P>#include<math.h><P>int matherr(struct exception *a)<BR>{<BR> return 1;<BR>}<BR> <BR> <BR> <P>函数名: memccpy<BR>功 能: 从源source中拷贝n个字节到目标destin中<BR>用 法: void *memccpy(void *destin, void *source, unsigned charch,<BR> unsigned n);<BR>程序例:<P>#include <string.h><BR>#include <stdio.h><P>int main(void)<BR>{<BR> char *src = "This is the source string";<BR> char dest[50];<BR> char *ptr;<P> ptr = memccpy(dest, src, 'c', strlen(src));<P> if (ptr)<BR> {<BR> *ptr = '\0';<BR> printf("The character was found: %s\n", dest);<BR> }<BR> else<BR> printf("The character wasn't found\n");<BR> return 0;<BR>}<BR> <BR> <P>函数名: malloc<BR>功 能: 内存分配函数<BR>用 法: void *malloc(unsigned size);<BR>程序例:<P>#include <stdio.h><BR>#include <string.h><BR>#include <alloc.h><BR>#include <process.h><P>int main(void)<BR>{<BR> char *str;<P> /* allocate memory for string */<BR> /* This will generate an error when compiling */<BR> /* with C++, use the new operator instead. */<BR> if ((str = malloc(10)) == NULL)<BR> {<BR> printf("Not enough memory to allocatebuffer\n");<BR> exit(1); /* terminate programif out of memory */<BR> }<P> /* copy "Hello" into string */<BR> strcpy(str, "Hello");<P> /* display string */<BR> printf("String is %s\n", str);<P> /* free memory */<BR> free(str);<P> return 0;<BR>}<BR> <BR> <BR> <P>函数名: memchr<BR>功 能: 在数组的前n个字节中搜索字符<BR>用 法: void *memchr(void *s, char ch, unsigned n);<BR>程序例:<P>#include <string.h><BR>#include <stdio.h><P>int main(void)<BR>{<BR> char str[17];<BR> char *ptr;<P> strcpy(str, "This is a string");<BR> ptr = memchr(str, 'r', strlen(str));<BR> if (ptr)<BR> printf("The character 'r' is at position:%d\n", ptr - str);<BR> else<BR> printf("The character was not found\n");<BR> return 0;<BR>}<BR> <P>函数名: memcpy<BR>功 能: 从源source中拷贝n个字节到目标destin中<BR>用 法: void *memcpy(void *destin, void *source, unsigned n);<BR>程序例:<P>#include <stdio.h><BR>#include <string.h><BR>int main(void)<BR>{<BR> char src[] = "******************************";<BR> char dest[] = "abcdefghijlkmnopqrstuvwxyz0123456709";<BR> char *ptr;<BR> printf("destination before memcpy: %s\n", dest);<BR> ptr = memcpy(dest, src, strlen(src));<BR> if (ptr)<BR> printf("destination after memcpy: %s\n", dest);<BR> else<BR> printf("memcpy failed\n");<BR> return 0;<BR>}<BR> <BR> <P>函数名: memicmp<BR>功 能: 比较两个串s1和s2的前n个字节, 忽略大小写<BR>用 法: int memicmp(void *s1, void *s2, unsigned n);<BR>程序例:<P>#include <stdio.h><BR>#include <string.h><P>int main(void)<BR>{<BR> char *buf1 = "ABCDE123";<BR> char *buf2 = "abcde456";<BR> int stat;<BR> stat = memicmp(buf1, buf2, 5);<BR> printf("The strings to position 5 are ");<BR> if (stat)<BR> printf("not ");<BR> printf("the same\n");<BR> return 0;<BR>}<BR> <BR> <P>函数名: memmove<BR>功 能: 移动一块字节<BR>用 法: void *memmove(void *destin, void *source, unsigned n);<BR>程序例:<P>#include <string.h><BR>#include <stdio.h><P>int main(void)<BR>{<BR> char *dest = "abcdefghijklmnopqrstuvwxyz0123456789";<BR> char *src = "******************************";<BR> printf("destination prior to memmove: %s\n", dest);<BR> memmove(dest, src, 26);<BR> printf("destination after memmove: %s\n",dest);<BR> return 0;<BR>}<BR> <BR> <BR> <P>函数名: memset<BR>功 能: 设置s中的所有字节为ch, s数组的大小由n给定<BR>用 法: void *memset(void *s, char ch, unsigned n);<BR>程序例:<P>#include <string.h><BR>#include <stdio.h><BR>#include <mem.h><P>int main(void)<BR>{<BR> char buffer[] = "Hello world\n";<P> printf("Buffer before memset: %s\n", buffer);<BR> memset(buffer, '*', strlen(buffer) - 1);<BR> printf("Buffer after memset: %s\n", buffer);<BR> return 0;<BR>}<BR> <BR> <P>函数名: mkdir<BR>功 能: 建立一个目录<BR>用 法: int mkdir(char *pathname);<BR>程序例:<P>#include <stdio.h><BR>#include <conio.h><BR>#include <process.h><BR>#include <dir.h><P>int main(void)<BR>{<BR> int status;<P> clrscr();<BR> status = mkdir("asdfjklm");<BR> (!status) ? (printf("Directory created\n")) :<BR> (printf("Unable to create directory\n"));⌨️ 快捷键说明
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