如何读取和打印issuance.csv数据结尾？

Question

I need to read data store in end of file and print it. My input file has many numbers, and I have to read last number, can any one help me??

int main()
{
    FILE *fp;
        fp = fopen("f:\\Issuance.csv", "a");
        if (!fp)
        {
            printf("can not open file \n");
            getchar();
            exit(1);
        }
        int Size = 30;
        char FileInfo[100];
                fseek( fp , 0 , SEEK_END);
                fread(FileInfo, 1, Size, fp);
                printf("%d",FileInfo);
}
fcloseall();
            }

Answer 1

You need to use the 2nd parameter of fseek() .

fseek(fp, -Size, SEEK_END);
fread(FileInfo, 1, Size, fp);
FileInfo[Size] = '\0'; // NULL terminate FileInfo; or declare as char FileInfo[100] = {0};
printf("%s", FileInfo);

Answer 2

To read the last number in a text file (which may have additional junk after it), starting from the beginning, attempt to read a number. If successful, save it, else toss 1 char . Continue until the end of the file.

// Read last number
int ReadLastNumber(FILE *inf, int default_value) {
  int last = default_value;
  int num;
  int cnt;
  rewind(inf);
  while ((cnt = fscanf(inf,"%d", &num)) != EOF) {
    if (cnt == 1) {
      last = num;
    } else {
      fgetc(inf);  // toss non-numeric char
    }
  }
  return last;
}

A more sane solution would fseek() to the end, search backwards for digits. Once some digits are found, continue backwards looking for digits, + or - . Something like the following untested code.

#include <ctype.h>
#include <stdbool.h>
#include <stdlib.h>

// Read last number
int ReadLastNumber2(FILE *inf, int default_value) {
  int last = 0;
  int place = 1;
  bool digit_found = false;
  long offset = -1;
  while (fseek(inf, offset, SEEK_CUR) == 0) {
    int ch = fgetc(inf);
    if (ch == EOF)  // Likely I/O error
      return default_value;
    if (isdigit(ch)) {
      digit_found = true;
      last += (ch - '0')*place;
      place *= 10;
      offset = -2;
    } else if (ch == '-') {
      return -last;
    } else if (digit_found) {
      return last;
    }
  }
  return default_value;
}

Not protected against int overflow.