11-12 标准IO之feof，ferror，clearerr_ferror返回值为1-CSDN博客

本文链接：https://blog.csdn.net/wenwen111111/article/details/58252190

本文介绍了标准IO中的feof函数用于检测文件是否到达结尾，ferror函数用于检查读写操作是否有错误，以及clearerr函数用于清除流错误的状态。通过fgetc返回值可以辅助判断文件尾部或错误情况。

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1. 当返回错误时，怎样判读是已经到达文件结尾，还是读错呢？

a. int feof(FILE *stream);

功能：判断是否已经到文件结束

参数：文件流

返回值：到文件结束，返回为非0，没有则返回0

b.int ferror(FILE *stream);

功能：判断是否读写错误

参数：文件流

返回值：是读写错误，返回为非0，不是则返回0

c.void clearerr(FILE *stream);

功能：清除流错误

参数：文件流

2. 通过检查fgetc的返回值，判断是文件尾还是出错

#include "stdio.h"

int main(int argc, char *argv[]){
	FILE *fp;
	int ret;
	
	fp = open("./a.c","w+");
	if(fp == NULL){
		printf("open file a.c error\n");
		return -1;
	}
	printf("open file a.c success\n");
	
	fputc('a',fp);
	rewind(fp);
	
	ret = fgetc(fp);
	printf("ret = %c\n",ret);
	
	ret = fgetc(fp);
	printf("ret = %d\n",ret);
	
	printf("1feof=%d,ferror=%d\n",feof(fp),ferror(fp));
	
	clearerr(fp);
	printf("2feof=%d,ferror=%d\n",feof(fp),ferror(fp));
	
	fclose(fp);
	
	return 0;
}

3. 通过检查fgets的返回值，判断是文件尾还是出错

#include "stdio.h"

int main(int argc, char *argv[]){
	FILE *fp;
	char buf[] = "hello linux\n";
	char readbuf[128] = {0};
	char *ret;
	
	fp = open("./a.c","w+");
	if(fp == NULL){
		printf("open file a.c error\n");
		return -1;
	}
	printf("open file a.c success\n");
	
	fput(buf,fp);
	rewind(fp);
	
	fgets(readbuf,128,fp);
	printf("1readbuf : %s\n",readbuf);
	
	memset(readbuf,128,0);
	
	ret = fgets(readbuf,128,fp);
	printf("2readbuf = %s,ret=%p\n",readbuf,ret);
	
	printf("feof=%d,ferror=%d\n",feof(fp),ferror(fp));
	
	fclose(fp);
	
	return 0;
}

4. 例 cat 命令的实现

#include "stdio.h"
#include "unistd.h"
#include "fcntl.h"
#include "string.h"

int main(int argc, char *argv[]){
	FILE *src_fp;
	int read_ret;
	
	if(argc < 2){
		printf("please input src file \n");
		return -1;
	}
	
	src_fp = fopen(argv[1],"r");
	if(src_fp == NULL){
		printf("open src file %s error \n",argv[1]);
		return -2;
	}
	
	while(1){
		read_ret = fgetc(src_fp);
		if(feof(src_fp)){
			printf("read file %s end \n",argv[1]);
			break;
		}
		fputc(read_ret,stdout);
	}
	
	fclose(src_fp);

	return 0;
}