Question

我试图完成此练习：使用fscanf()和fprintf()函数执行一个程序，编写从文件输入中获取的一些数字，逐个读取值，打印增加1的值并在文件中重写它们。

这是我做的：

include <stdio.h>
#include <cstdlib>

int main()
{
    FILE *fp_1, *fp_2;
    int n, num, num_inc, i;

    fp_1 = fopen("output.txt", "w");
    if (fp_1 == NULL) {
        printf("Error");
        return 1;
    }
    printf("How many values you want to write? ");
    scanf("%i", &n);
    for(i=0; i<n; i++) {
        printf("Write the %i number: ", i+1);
        scanf("%i", &num);
        fprintf(fp_1, " %i ", num);
    }
    printf("Values read from file:\n");
    fp_2 = fopen("output.txt", "r");
    if(fp_2 == NULL) {
        printf("Error");
        return 2;
    }
    i = 0;
    while(!feof(fp_2) && i<n) {
        fscanf(fp_2, "  %i  ", &num);
        num_inc = num+1;
        fprintf(fp_1, "  %i  ", num_inc);
        printf("%i value read is: %i\n", i+1, num_inc);
        i++;
    }

    fclose(fp_1);
    fclose(fp_2);
    system("pause");
}

这是输出：

How many values you want to write? 5
Write the 1 number: 32
Write the 2 number: 124
Write the 3 number: 55646
Write the 4 number: 32
Write the 5 number: 112

Values read from file:

1 value read is: 113.

问题在于只读取了一个值。

谢谢！

Answer 1

尝试在fp_1上执行fclose，然后再次以fp_2打开文件。

Answer 2

关键是使用另一个文件进行第二次输出。

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

int main()
{
    FILE *input_file, *output_file;
    int n, num, num_inc, i;

    input_file = fopen("input.txt", "w+"); // Actually it is the input for the next step.
    if (input_file == NULL) {
        printf("Error");
        return 1;
    }
    printf("How many values you want to write? ");
    scanf("%i", &n);
    for (i = 0; i < n; i++) {
        printf("Write the %i number: ", i + 1);
        scanf("%i", &num);
        fprintf(input_file, " %i ", num);
    }

    rewind(input_file); // Rewind to the beginning to perform reading.

    output_file = fopen("output.txt", "w"); // The name of the output file (must be different from the input one).
    if (output_file == NULL) {
        printf("Error");
        return 2;
    }

    printf("Values read from file:\n");
    i = 0;
    while (!feof(output_file) && i < n) {
        fscanf(input_file, "  %i  ", &num);
        num_inc = num + 1;
        fprintf(output_file, "  %i  ", num_inc);
        printf("%i value read is: %i\n", i+1, num_inc);
        i++;
    }

    fclose(input_file);
    fclose(output_file);
    system("pause");
}

从文件写入和读取的问题

2 个答案: