从两个不同的文件获取输入 [英] Getting inputs from two different files

问题描述

我一直在研究这个问题:

I've been working on this problem:

C程序，它可以从2个文件&中合并行打印结果

C Program that Merges Lines Alternatively from 2 Files & Print Result

这是我编写的代码:

#include <stdio.h>
#include <stdlib.h>
int main(){
    FILE *fp;
    FILE *fp1;
    FILE *fp2;
    fp=fopen ("sample4.txt","r");
    fp1=fopen ("sample3.txt","r");
    fp2= fopen ("output.txt","w");
    char a[100];
    char b[100];
    while (fgets(a,100,fp1)!=NULL||fgets (b,100,fp)!=NULL){
            printf("%s",a);
            printf ("%s",b);
    }
    return 0;
}

但是我没有得到想要的输出.有人可以解释为什么吗?

However I am not getting desired output. Can someone explain why?

PS:还有另一个问题要求:如果一个文件的行数少于另一个文件，则应简单地打印较大文件中的其余行.

PS: There is another problem requirement: If one file has less number of lines than the other, the remaining lines from the larger file should be simply printed.

推荐答案

但是我没有得到想要的输出.有人可以解释为什么吗?

However I am not getting desired output. Can someone explain why?

fgets(a，100，fp1)！= NULL || fgets(b，100，fp)！= NULL 在以下情况下不评估第二个 fgets() || 的左侧为true(由于成功读取).

fgets(a,100,fp1)!=NULL||fgets (b,100,fp)!=NULL does not evaluate the 2nd fgets() when the left-hand-side of the || is true (due to a successful read).

还有另一个问题要求:如果一个文件的行数少于另一个文件，则应简单地打印较大文件中的其余行.

There is another problem requirement: If one file has less number of lines than the other, the remaining lines from the larger file should be simply printed.

而不是尝试从已返回 NULL 的流中重新读取，而是考虑每个流的标志:

Rather than try to re-read from a stream that has already returned NULL, consider a flag per stream:

// OP may want to stop before here if an fopen() failed.

bool ok_a = fp1;  // Did file open OK?
bool ok_b = fp;
char a[100];
char b[100];

while (ok_a || ok_b) {
   // OK to read and then set the flag per the read result.
   if (ok_a && (ok_a = fgets(a, sizeof a, fp1)) {
     printf("%s",a);
   }
   if (ok_b && (ok_b = fgets(b, sizeof b, fp)) {  // ***
     printf("%s",b);
   }
}

// Optional
printf("a: EOF:%d, Error:%d\n", feof(fp1), ferror(fp1));
printf("b: EOF:%d, Error:%d\n", feof(fp) , ferror(fp));

// Good to close the files
// A fclose() should NOT get called if the FILE *  pointer is NULL.
if (fp)  fclose(fp);
if (fp1) fclose(fp1);
if (fp2) fclose(fp2);

---

OP可能希望附加代码来处理以下情况:由于行长，嵌入， fgets()的结果不包含'\ n'空字符或最后一行.

---

OP might want additional code to handle the cases when the result of fgets() does not contain a '\n' due to being a long line, an embedded null character or the last line.

***请注意，不需要第二个缓冲区，可以重新使用 a [] .

*** Note that a 2nd buffer is not needed, could re-use a[].

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