Question

经过不懈地寻找解释之后，我决定在stackoverflow上问一些大师。因此，我目前正在尝试从名为data.txt的文件中逐行读取每个输入。该程序使用简单的scanf等可以完美运行，但是当我想从文件中读取输入值时，该程序仅读取txt的前三行，并且在无限循环中不断重复。我的代码如下所示。我保留了大部分代码，以防其他人想使用它。程序将无限读取1、12、0。示例data.txt文件如下所示

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

// Global variables
char *Hstring = NULL;
int maxLength, parity;
char *temp = NULL;
int userChoice = 0;


void option1() {
    // User inputs length and even or odd parity bit 
    printf("\n*** Maximum Code Length: %d", maxLength);
    //scanf("%d",&maxLength);
    printf("\n*** Parity: %d", parity);
    //scanf("%d",&parity);
   // allocate memory for hamming string based on maximum length and 
   //size of character element
    Hstring = (char *)malloc(maxLength * sizeof(char));
    return;
}

void option2() {
    /* declare local vars */
    int aLength, k, parBits, parValue, errorPos, i, j;
    /* prompt for hamming code as a "string"*/
    printf("\nEnter the Hamming Code: ");
    scanf("%s", Hstring);
    temp = Hstring;
    aLength = strlen(Hstring);
    parBits = ceil(log(aLength) / log(2));
}

int main() {
    FILE *fp;
    fp = fopen("data.txt", "r");
    if (fp == NULL) {
        printf("ERROR OPENING THE FILE\n");
    }
    fscanf(fp, "%d %d %d", &userChoice, &maxLength, &parity);
    //end file open

    while (userChoice != 3) {
        printf("\nEnter Selection: %d", userChoice);
        //scanf("%d",&userChoice);
        switch (userChoice) {
        case 1:option1();
            break;
        case 2:option2();
            break;
        case 3:
            printf("\n*** Program Terminated Normally\n");
            break;
        default: printf("invalid input please input another number\n\n");
            break;
        }
    }
    /* print out menu, prompt for choice, and call appropriate procedure
    until user quits */

    return 1;
}

SAMPLE data.txt

代码在读取option1（）中的第三个整数（奇偶校验）时开始循环

任何帮助将不胜感激。谢谢！

Answer 1

您永远不会在while循环中修改userChoice，因此它将永远循环。

无论如何，即使您在while循环中使用了fscanf，因此读取了整个文件，直到找到userChoice == 3，也要让循环终止条件仅取决于内容是一个坏主意对于文件，您还应该检查fscanf的结果以确认文件是否终止。您的示例数据仍将永远循环，因为其中不包含3。

Answer 2

https://stackoverflow.com/a/53475412/4386427的答案正确地描述了问题，即您有一个无限循环，因为userChoice仅被读取了一次。

这里是修复建议。

int main() {
    FILE *fp;
    fp = fopen("data.txt", "r");
    if (fp == NULL) {
        printf("ERROR OPENING THE FILE\n");
    }


    while (userChoice != 3) {

        // Check that exactly 3 items are read from the file.
        // If not terminate the program
        if (fscanf(fp, "%d %d %d", &userChoice, &maxLength, &parity) != 3) {
            printf("Illegal input from file or EOF. Terminating program\n");
            break;
        }

        switch (userChoice) {
        case 1:option1();
            break;
        case 2:option2();
            break;
        case 3:
            printf("\n*** Program Terminated Normally\n");
            break;
        default: printf("invalid input please input another number\n\n");
            break;
        }
    }

    return 1;
}

从输入文件读取输入，不断陷入无限循环

2 个答案: