环境变量

环境变量

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

extern char**environ;

main(int args,char**argv,char**arge)

{

printf("%s\n",getenv("PATH"));

printf("%s\n",getenv("LOGNAME"));

/*

while(environ && *environ)

{

printf("%s\n",*environ);

environ++;

}

*/

/*

while(arge && *arge)

{

printf("%s\n",*arge);

arge++;

}

int i=0;

while(arge && arge[i])

{

printf("%s\n",arge[i++]);

}

*/

}

read &&open 函数

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <fcntl.h>

#include <string.h>

main()

{

char name[20];

int  age;

float score;

char sex;

char *filename="a.dat";

int fd;

fd=open(filename,O_RDWR);

if(fd==-1)

{

perror("open error");

exit(-1);

}

int r;

while(1)

{

r=read(fd,name,sizeof(name));

if(r<=0) break;

r=read(fd,&age,sizeof(int));

r=read(fd,&score,sizeof(score));

r=read(fd,&sex,sizeof(char));

printf("%s,%d,%5.2f,%c\n",

       name,age,score,sex);

}

close(fd);

}

write&&函数 

#include <stdio.h>

#include <unistd.h>

#include <fcntl.h>

#include <stdlib.h>

#include <string.h>

main()

{

int fd;

char *filename="a.dat";

char name[20];

int  age;

float score;

char sex;

  fd=open(filename,O_RDWR|O_CREAT|O_EXCL,0666);

if(fd==-1)

{

perror("open error");

exit(-1);

}

bzero(name,sizeof(name));

//memset(name,0,sizeof(name));

memcpy(name,"tom",3);

age=20;

score=89.99f;

sex='m' ;

write(fd,name,sizeof(name));

write(fd,&age,sizeof(age));

write(fd,&score,sizeof(score));

write(fd,&sex,sizeof(sex));

bzero(name,sizeof(name));

memcpy(name,"Jack",4);

age=18;

score=99.88f;

sex='f';

write(fd,name,sizeof(name));

write(fd,&age,sizeof(age));

write(fd,&score,sizeof(score));

write(fd,&sex,sizeof(sex));

close(fd);

}

printf("%*2$.*3$f\n",12345.6789,40,20);