linux cプログラミングファイルIO

記事の内容は
21日学通linux cプログラミング
主な関数:
開く:fopen fdopen freopen
閉じる:fclose
読み込みよみとり:getc fgets fread
書き込み:putc fputc fputs fwrite
読み取り文字

#include <stdio.h>
#include <errno.h>

main()
{
   FILE * fp;
   extern int errno; 
   char file[]="/root/a1.txt";
   fp=fopen(file,"r");
   int i;
   char a;
   if(fp==NULL)
   {
   	  printf("cant't open file %s.
",file);
   	  printf("errno：%d
",errno);
   	  printf("ERR  ：%s
",strerror(errno));
   	  return;
   	}
   	else
   	{
   		printf("%s was opened.
",file);   		
	}
	for(i=0;i<10;i++)
	{
		a=getc(fp);
		if(a==EOF)
		{
			break;
		}
		printf("%c",a);
   }
   printf("
");
   fclose(fp);   
}

文字列の読み込み

#include <stdio.h>
#include <errno.h>

main()
{
   FILE * fp;
   extern int errno; 
   char file[]="/root/a1.txt";
   fp=fopen(file,"r");
   int i;
   char a[5];
   if(fp==NULL)
   {
   	  printf("cant't open file %s.
",file);
   	  printf("errno：%d
",errno);
   	  printf("ERR  ：%s
",strerror(errno));
   	  return;
   	}
   	else
   	{
   		printf("%s was opened.
",file);   		
	}
    fgets(a,5,fp);
   printf("%s
",a);
   fclose(fp);   
}

データの読み込み

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
struct stu
{
	char name[10];
	int age;	
};
main()
{
   struct stu mystu[3];
   FILE * fp;
   extern int errno; 
   char file[]="/root/a1.txt";
   int i,j;
 
   fp=fopen(file,"a+");
   if(fp==NULL)
   {
   	  printf("cant't open file %s.
",file);
   	  printf("errno：%d
",errno);
   	  printf("ERR  ：%s
",strerror(errno));
   	  return;
   	}
   	else
   	{
   		printf("%s was opened.
",file);   		
	}
    i=fread(mystu,sizeof(struct stu),3,fp);
    printf("%d students was read.
",i);
    close(fp);
}

書き込み文字

#include <stdio.h>
#include <errno.h>

main()
{
   FILE * fp;
   extern int errno; 
   char file[]="/root/a1.txt";
   char txt[5]="hello";
   int i=0;
   fp=fopen(file,"a+");
   if(fp==NULL)
   {
   	  printf("cant't open file %s.
",file);
   	  printf("errno：%d
",errno);
   	  printf("ERR  ：%s
",strerror(errno));
   	  return;
   	}
   	else
   	{
   		printf("%s was opened.
",file);   		
	}
	
   
   for(i=0;i<5;i++)
   {
   	  putc(txt[i],fp);
   	  printf("%c",txt[i]);

   	}   	
   	fclose(fp);    
}

書き込み文字列

#include <stdio.h>
#include <errno.h>

main()
{
   FILE * fp;
   extern int errno; 
   char file[]="/root/a1.txt";
   char *txt="hello";
   int i;
   fp=fopen(file,"a+");
   if(fp==NULL)
   {
   	  printf("cant't open file %s.
",file);
   	  printf("errno：%d
",errno);
   	  printf("ERR  ：%s
",strerror(errno));
   	  return;
   	}
   	else
   	{
   		printf("%s was opened.
",file);   		
	}
 
   	i=fputs(txt,fp);
   	{
   		printf("%d char was written.
",i);
	}
	close(fp);
}

データの書き込み

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
struct stu
{
	char name[10];
	int age;	
};
main()
{
   struct stu mystu[3];
   FILE * fp;
   extern int errno; 
   char file[]="/root/a1.txt";
   int i;
   strcpy(mystu[0].name,"Jim");
   mystu[0].age=14;
   strcpy(mystu[0].name,"Jam");
   mystu[1].age=14;  
   strcpy(mystu[0].name,"Lily");
   mystu[2].age=19; 
   fp=fopen(file,"a+");
   if(fp==NULL)
   {
   	  printf("cant't open file %s.
",file);
   	  printf("errno：%d
",errno);
   	  printf("ERR  ：%s
",strerror(errno));
   	  return;
   	}
   	else
   	{
   		printf("%s was opened.
",file);   		
	}
 
    i=fwrite(mystu,sizeof(mystu),3,fp);
    printf("%d students was written.
",i);
    close(fp);
}