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每天进步一点点-->函数fseek() 使用方法

在阅读代码时,遇到了非常早之前用过的fseek(),非常久没实用了,有点陌生,写出来以便下次查阅。

函数功能是把文件指针指向文件的开头,须要包括头文件stdio.h

fseek
  函数名: fseek
  功 能: 重定位流上的文件指针
  用 法: int fseek(FILE *stream, long offset, int fromwhere);
  描 述: 函数设置文件指针stream的位置。假设运行成功,stream将指向以fromwhere为基准,偏移offset个字     节的位置。假设运行失败(比方offset超过文件自身大小),则不改变stream指向的位置。
  返回值: 成功,返回0,否则返回其它值。
  fseek position the file position pointer for the file referenced by stream to the byte location calculated by offset.
  程序例:
  

#include <stdio.h>  long filesize(FILE *stream);  int main(void)  {    FILE *stream;    stream = fopen("MYFILE.TXT", "w+");    fprintf(stream, "This is a test");    printf("Filesize of MYFILE.TXT is %ld bytes\n", filesize(stream));    fclose(stream);    return 0;  }  long filesize(FILE *stream)  {    long curpos, length;    curpos = ftell(stream);    fseek(stream, 0L, SEEK_END);    length = ftell(stream);    fseek(stream, curpos, SEEK_SET);    return length;  }


  int fseek( FILE *stream, long offset, int origin );
  第一个參数stream为文件指针
  第二个參数offset为偏移量,整数表示正向偏移,负数表示负向偏移
  第三个參数origin设定从文件的哪里開始偏移,可能取值为:SEEK_CUR、 SEEK_END 或 SEEK_SET
  SEEK_SET: 文件开头
  SEEK_CUR: 当前位置
  SEEK_END: 文件结尾

  当中SEEK_SET,SEEK_CUR和SEEK_END和依次为0,1和2.
  简言之:
  fseek(fp,100L,0);把fp指针移动到离文件开头100字节处;
  fseek(fp,100L,1);把fp指针移动到离文件当前位置100字节处;
  fseek(fp,100L,2);把fp指针退回到离文件结尾100字节处。
  使用实例:

  #include <stdio.h>  #define N 5  typedef struct student {   long sno;   char name[10];   float score[3];  } STU;  void fun(char *filename, STU n)  {   FILE *fp;   fp = fopen(filename, "rb+");   fseek(fp, -1L*sizeof(STU),SEEK_END);  fwrite(&n, sizeof(STU), 1, fp);  fclose(fp);  }  void main()  {    STU t[N]={ {10001,"MaChao", 91, 92, 77}, {10002,"CaoKai", 75, 60, 88},    {10003,"LiSi", 85, 70, 78}, {10004,"FangFang", 90, 82, 87},    {10005,"ZhangSan", 95, 80, 88}};    STU n={10006,"ZhaoSi", 55, 70, 68}, ss[N];    int i,j; FILE *fp;    fp = fopen("student.dat", "wb");    fwrite(t, sizeof(STU), N, fp);    fclose(fp);    fp = fopen("student.dat", "rb");    fread(ss, sizeof(STU), N, fp);    fclose(fp);    printf("\nThe original data :\n\n");    for (j=0; j<N; j++)    {     printf("\nNo: %ld Name: %-8s Scores: ",ss[j].sno, ss[j].name);     for (i=0; i<3; i++) 
     printf("%6.2f ", ss[j].score[i]);     printf("\n");    }    fun("student.dat", n);    printf("\nThe data after modifing :\n\n");    fp = fopen("student.dat", "rb");    fread(ss, sizeof(STU), N, fp);    fclose(fp);    for (j=0; j<N; j++)    {     printf("\nNo: %ld Name: %-8s Scores: ",ss[j].sno, ss[j].name);     for (i=0; i<3; i++) 
     printf("%6.2f ", ss[j].score[i]);     printf("\n");    }  }



 

每天进步一点点--&gt;函数fseek() 使用方法