【C】从文件中读取数字

假设src.txt是包含各种ascii字符的文本文件。请提取src.txt文本中的数字，并保存在dst.txt文件中。数字之间用空格隔开。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define IN 0
#define OUT 1

/*从名为src文件中找到数字，将其写入到名字为dst的文件中*/
int write_digit(char *dst, char *src)
{
    FILE *fp1;
    FILE *fp2;
    if( !(fp1 = fopen(src,"r")))
    {
        fprintf(stderr,"failed to open %s
",src);
        exit(-1);
    }
    if( !(fp2 = fopen(dst,"w+")))
    {
        fprintf(stderr,"failed to open %s
",dst);
        exit(-1);
    }
    int ch;
    int state = OUT;
    while( (ch = fgetc(fp1))!=EOF)
    {
        if( ch < '0' || ch > '9')
        {
            if(IN == state)
            {
                fputc(' ',fp2);
            }
            state = OUT;
        }
        else 
        {
            fputc(ch,fp2);
            state = IN;
        }
    }
    fclose(fp1);
    fclose(fp2);
    return 0;
}

int main()
{
    char *s1 = "src.txt";
    char *s2 = "dst.txt";
    write_digit(s2, s1);
    return 0;  
}