C 编程：从文件中读取并打印到控制台

Question

Good evening,

I know there's similar questions, which I have been sifting through, but this particular issue seems to be unique.

I am attempting to figure out how to simply read a text file into a string, and then write the string to standard output. I tried this code, but nothing is happening in the console when I call puts(). The file.txt generates properly with "hello" written, but the last if statement doesn't seem to work for some reason since it does not reach my test condition. How can I make this functional?

This was the code given by many, many examples online, only slightly modified:

#include <stdio.h>

int main()
{
    FILE *fp;
    char str[60];

    fp = fopen("file.txt","w+");
    fprintf(fp,"%s","hello");
    if(fp==NULL){
        perror("Error opening file");
        return(-1);
    }
    if (fgets (str, 60, fp)!=NULL)
        puts(str);
        printf("%s","test");
    fclose(fp);
return 0;
}

Answer 1

写入文件后，必须fclose() fp并重新fopen()文件以进行读取。

Answer 2

By the time you call fgets() , the file pointer is already at end of file. Add a call to rewind(fp) before your fgets() .

Oh, also when you're opening the file, put your check for fp==NULL before the call to fprintf() .

Answer 3

There is easiest way to read from file and print on console. use freopen() function to open file and read it using basic STD I/O.

I rewrite your solution in my way.

 #include <stdio.h>

 int main()
 {
    char str[60];
    FILE* x = freopen("file.txt","r",stdin);
    if(x==NULL){
        printf("Error opening file");
        return(-1);
    }
    while(fgets (str, 60,stdin)){
        puts(str);
    }
    return 0;
}