任何人都可以帮忙吗？我正在尝试从文件中读取数据，但它只是吐出垃圾

【问题标题】：Can anyone help? I am trying to read data from a file but its just spitting out garbage任何人都可以帮忙吗？我正在尝试从文件中读取数据，但它只是吐出垃圾
【发布时间】：2022-10-09 11:14:07
【问题描述】：

我正在尝试从文件 hw4.data 中读取并查看它是否有名称。用户通过命令行参数输入名称。一切正常，但我无法让文件在函数之间正确传递。作业要求我在 main 中定义文件并在 SCAN 和 LOAD 之间传递它。

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

struct _data {
    char name[20];
    long number;
};

int SCAN(FILE *(*stream)) { // skim through the file and find how many entries there are
    int size = 0;
    char s_temp[100];
    long l_temp;
    while (1) {
        fscanf(*stream, "%s %ld", s_temp, &l_temp);
        if (feof(*stream)) break;
        size++;
    }
    return size;
}

struct _data* LOAD(FILE *stream, int size) { // loop through the file and load the entries into the main data array
    struct _data* d = malloc(size * sizeof(struct _data));
    int i;
    for (i = 0; i < size; i++) {
        fscanf(stream, "%s %ld", d[i].name, &d[i].number);
    }
    return d;
}

void SEARCH(struct _data *BlackBox, char* name, int size) { // loop through the array and search for the right name

    int i;
    int found = 0;
    for (i = 0; i < size; i++) {
        printf("%s %s\n", BlackBox[i].name, name);
        if (strcmp(BlackBox[i].name, name) == 0) {
            printf("*******************************************\nThe name was found at the %d entry.\n*******************************************\n", i);
            found = 1;
            break;
        }
    }
    if (found == 0) {
        printf("*******************************************\nThe name was NOT found.\n*******************************************\n");
    }
}

void FREE(struct _data* BlackBox, int size) { // free up the dynamic array
    free(BlackBox);
}

int main(int argv, char* argc[]) {
    
    if (argv == 2) {
        printf("The argument supplied is %s\n", argc[1]);

        FILE* file = fopen("./hw4.data", "r");

        int size = SCAN(&file);
        struct _data* data = LOAD(&file, size);

        SEARCH(data, argc[1], size);

        fclose(file);
        return 0;
    } else {
        printf("*******************************************\n* You must include a name to search for.*\n*******************************************\n");
        return 0;
    }
}

这是hw4.data的格式

ron 7774013
jon 7774014
tom 7774015
won 7774016

【问题讨论】：

  • 您的编译器应该向您抱怨：您将 FILE ** 传递给 LOAD 函数，但它只需要一个 FILE * 参数。为什么你还是通过&amp;file？那有什么意义呢？
  • 您必须始终检查 fscanf 等函数的返回值，以确保它们成功。
  • 另外，除非第一个参数是格式字符串，否则不要使用printf，否则使用fputs。
  • 在SCAN 中，删除feof。替换为：if (fscanf(*stream, "%s %ld", s_temp, &amp;l_temp) != 2) break; 请注意，在调用SCAN 之后，您应该这样做：rewind(file);。否则，LOAD 只会看到 [立即] EOF。而且，正如其他人所提到的，只需将file 传递给SCAN/LOAD 和不是&amp;file。第三，添加对来自fopen（例如）if (file == NULL) { perror("fopen"); exit(1); } 的空返回的检查

标签： c file


【解决方案1】：

几个问题：

  1. 在SCAN 中，删除feof。替换为：if (fscanf(*stream, "%s %ld", s_temp, &amp;l_temp) != 2) break;
  2. 请注意，在调用SCAN 之后，您应该执行以下操作：rewind(file);。否则，LOAD 只会看到 [立即] EOF。
  3. 正如其他人所提到的，只需将file 传递给SCAN/LOAD 和不是&amp;file。
  4. 添加对来自fopen（例如）if (file == NULL) { perror("fopen"); exit(1); } 的空返回的检查

    风格上：

    1. 如果您有描述函数的注释，请将其放在函数上方的行中。
    2. 尽量将行保持在 80 个字符以内

      这是重构后的代码：

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

struct _data {
    char name[20];
    long number;
};

// skim through the file and find how many entries there are
int
SCAN(FILE *stream)
{
    int size = 0;
    char s_temp[100];
    long l_temp;

    while (1) {
        if (fscanf(stream, "%s %ld", s_temp, &l_temp) != 2)
            break;
        size++;
    }

    return size;
}

// loop through the file and load the entries into the main data array
struct _data *
LOAD(FILE *stream, int size)
{
    struct _data *d = malloc(size * sizeof(struct _data));
    int i;

    for (i = 0; i < size; i++) {
        fscanf(stream, "%s %ld", d[i].name, &d[i].number);
    }

    return d;
}

// loop through the array and search for the right name
void
SEARCH(struct _data *BlackBox, char *name, int size)
{

    int i;
    int found = 0;

    for (i = 0; i < size; i++) {
        printf("%s %s
", BlackBox[i].name, name);
        if (strcmp(BlackBox[i].name, name) == 0) {
            printf("*******************************************
");
            printf("The name was found at the %d entry.
", i);
            printf("*******************************************
");
            found = 1;
            break;
        }
    }
    if (found == 0)
        printf("*******************************************
"
            "The name was NOT found.
"
            "*******************************************
");
}

// free up the dynamic array
void
FREE(struct _data *BlackBox, int size)
{
    free(BlackBox);
}

int
main(int argv, char *argc[])
{

    if (argv == 2) {
        printf("The argument supplied is %s
", argc[1]);

        FILE *file = fopen("./hw4.data", "r");
        if (file == NULL) {
            perror("fopen");
            exit(1);
        }

        int size = SCAN(file);
        rewind(file);
        struct _data *data = LOAD(file, size);

        SEARCH(data, argc[1], size);

        fclose(file);
    }
    else
        printf("*******************************************
"
            "* You must include a name to search for.*
"
            "*******************************************
");

    return 0;
}

      使用realloc，我们可以将SCAN 和LOAD 组合成一个函数：

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

struct _data {
    char name[20];
    long number;
};

// loop through the file and load the entries into the main data array
struct _data *
LOAD(FILE *stream, int *sizep)
{
    struct _data *all = NULL;
    struct _data *d;
    int size = 0;
    int capacity = 0;

    while (1) {
        if (size >= capacity) {
            capacity += 10;
            all = realloc(all,sizeof(*all) * capacity);
            if (all == NULL) {
                perror("realloc");
                exit(1);
            }
        }

        d = &all[size++];

        if (fscanf(stream, "%s %ld", d->name, &d->number) != 2)
            break;
    }

    // trim to size actually used
    all = realloc(all,sizeof(*all) * size);

    *sizep = size;

    return all;
}

// loop through the array and search for the right name
void
SEARCH(struct _data *BlackBox, char *name, int size)
{

    int i;
    int found = 0;

    for (i = 0; i < size; i++) {
        printf("%s %s
", BlackBox[i].name, name);
        if (strcmp(BlackBox[i].name, name) == 0) {
            printf("*******************************************
");
            printf("The name was found at the %d entry.
", i);
            printf("*******************************************
");
            found = 1;
            break;
        }
    }
    if (found == 0)
        printf("*******************************************
"
            "The name was NOT found.
"
            "*******************************************
");
}

// free up the dynamic array
void
FREE(struct _data *BlackBox, int size)
{
    free(BlackBox);
}

int
main(int argv, char *argc[])
{

    if (argv == 2) {
        printf("The argument supplied is %s
", argc[1]);

        FILE *file = fopen("./hw4.data", "r");
        if (file == NULL) {
            perror("fopen");
            exit(1);
        }

        int size;
        struct _data *data = LOAD(file, &size);

        SEARCH(data, argc[1], size);

        fclose(file);
    }
    else
        printf("*******************************************
"
            "* You must include a name to search for.*
"
            "*******************************************
");

    return 0;
}

【讨论】：

    【解决方案2】：

    我必须使用rewind() 来重置文件，以便LOAD() 从文件开头读取并提供良好的数据。

    【讨论】：

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