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社区首页 >问答首页 >在C中使用读取文件时遇到的问题

问在C中使用读取文件时遇到的问题
EN

Stack Overflow用户
提问于 2022-05-15 14:10:25
回答 2查看 257关注 0票数 0

我编写了下面的代码来将文件读入结构中，但是当我运行这段代码时，输出可以在下面的文本中看到。我想把这个文件读入结构中，每一个字符块都有数字、名字、姓氏等。原始文件也如下所示。

代码语言：javascript
复制
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
struct StudentInfo{
    char studentNumber[20];
    char studentName[20];
    char studentSurname[20];
    char department[20];
    char eMail[20];
};
int main(int argc, char *argv[]) {
    
    //Declarations
    char firstFileName[20];
    char secondFileName[20];
    char operationType[2];
    char data[100];
    struct StudentInfo *studentInfo=(struct StudentInfo*) malloc(sizeof(struct StudentInfo));
    FILE *firstFile;
    FILE *secondFile;
    printf("Enter the first file name: ");
    scanf("%s",firstFileName);
    printf("Enter the second file name: ");
    scanf("%s",secondFileName);
    printf("Enter the operation type (-i, -u):");
    scanf("%s",operationType);
    
    if(strcmp(operationType,"-i")==0){
    
        firstFile = fopen(strcat(firstFileName,".txt"),"r");
        while(!feof(firstFile)){
            fread(studentInfo,sizeof(struct StudentInfo),1,firstFile);
            printf("%s",studentInfo->studentNumber);
        }
    }
    if(strcmp(operationType,"-u")==0){
        printf("%s",secondFileName);    
    }
    fclose(firstFile);

    /*
    while(!feof(firstFile)){
        students[1]->studentNumber = 
    }
    fclose(firstFile);*/
    
}

文件的原始内容是：

代码语言：javascript
复制
Ogrenci No;Ogrenci;Program;Sinif;Email;Status
10000000000;EDA NUR   YILMAZ;Computer Engineering;4;enur.yilmaz@tedu.edu.tr;
10000000010;FEYZA  NUR  DUMAN;Computer Engineering;2;fnur.duman@tedu.edu.tr;
20000000010;GOKHAN  YAMAC;Computer Engineering;2;gokhan.yamac@tedu.edu.tr;
30000000030;CEREN  AYDINLI;Computer Engineering;2;ceren.aydinli@tedu.edu.tr;
30000000010;DURU  YAMAC;Computer Engineering;3;duru.yamac@tedu.edu.tr;
40000000010;SEVIL TERZI;Computer Engineering;2;sevil.terzi@tedu.edu.tr;
50000000010;EREN  AYDIN;Computer Engineering;2;eren.aydin@tedu.edu.tr;
50000000020;YAMAC    YILMAZ;Computer Engineering;2;yamac.yilmaz@tedu.edu.tr;
60000000020;EDANUR    YILMAZ;Computer Engineering;2;edanur.yilmaz@tedu.edu.tr;
70000000010;GOKHAN YAMAC;Computer Engineering;2;gokhan.yamac18@tedu.edu.tr;

我代码的输出是：

代码语言：javascript
复制
Ogrenci No;Ogrenci;Program;Sinif;Email;Status
10000000000;EDA NUR   YILMAZ;Computer Engineering;4;enPI_K³Æ_aj©ur.yilmaz@tedu.edu.tr;
10000000010;FEYZA  NUR  DUMAN;Computer Engineering;2;fnur.duman@tedu.edu.tr;
PI_K³Æ_aj©20000000010;GOKHAN  YAMAC;Computer Engineering;2;gokhan.yamac@tedu.edu.tr;
30000000030;CEREN  AYDINLPI_K³Æ_aj©I;Computer Engineering;2;ceren.aydinli@tedu.edu.tr;
30000000010;DURU  YAMAC;Computer Engineering;3;dPI_K³Æ_aj©uru.yamac@tedu.edu.tr;
40000000010;SEVIL TERZI;Computer Engineering;2;sevil.terzi@tedu.edu.tr;
50000PI_K³Æ_aj©000010;EREN  AYDIN;Computer Engineering;2;eren.aydin@tedu.edu.tr;
50000000020;YAMAC    YILMAZ;ComputPI_K³Æ_aj©er Engineering;2;yamac.yilmaz@tedu.edu.tr;
60000000020;EDANUR    YILMAZ;Computer Engineering;2;edanuPI_K³Æ_aj©r.yilmaz@tedu.edu.tr;
70000000010;GOKHAN YAMAC;Computer Engineering;2;gokhan.yamac18@tedu.edu.tr;
nuPI_K³Æ_aj©
c
file
EN

回答 2

Stack Overflow用户

发布于 2022-05-15 17:57:10

环路

代码语言：javascript
复制
while(!feof(firstFile)){
    fread(studentInfo,sizeof(struct StudentInfo),1,firstFile);
    printf("%s",studentInfo->studentNumber);
}

是错误的，有几个原因：

循环条件是错误的。有关更多信息，请参见以下问题：Why is “while ( !feof (file) )” always wrong?

线

代码语言：javascript
复制
fread(studentInfo,sizeof(struct StudentInfo),1,firstFile);

将尝试从文件中准确读取sizeof(struct StudentInfo)字节，即100个字节。换句话说，你的程序假设每一行都是100字节长，下一个条目也就是100字节长。您的程序还假设这100字节长的条目之间没有任何内容(也没有换行符)。此外，您的程序假设文件中的每个字符串中都有一个空终止字符(因为稍后您试图将它们打印为空终止字符串)。所有这三个假设都是错误的。

您实际拥有的是一个文件，其中每个条目由换行符分隔。条目的字段具有可变长度(而不是固定长度为20)，这些字段由;字符分隔。因此，使用函数fgets一次读取一行比较合适，并使用strtok将该行划分为单独的字段：

代码语言：javascript
复制
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct StudentInfo
{
    char studentNumber[20];
    char studentName[20];
    char department[20];
    char unknown[20];
    char eMail[20];
};

int main( void )
{
    FILE *fpInput;
    char line[400];
    struct StudentInfo si;

    //open input file
    fpInput = fopen( "input.txt", "r" );
    if ( fpInput == NULL )
    {
        fprintf( stderr, "Error opening file!\n" );
        exit( EXIT_FAILURE );
    }

    //ignore first line of input
    fgets( line, sizeof line, fpInput );

    //read one line of input per loop iteration
    while ( fgets( line, sizeof line, fpInput ) != NULL )
    {
        char *p;

        //attempt to find newline character
        p = strchr( line, '\n' );

        //make sure entire line was read, and remove newline
        //character if necessary
        if ( p == NULL )
        {
            //a missing newline character is ok on end-of-file
            if ( !feof(fpInput) )
            {
                fprintf( stderr, "Line too long for input buffer!\n" );
                exit( EXIT_FAILURE );
            }
        }
        else
        {
            //remove newline character from input
            *p = '\0';
        }

        //attempt to read student number
        p = strtok( line, ";" );
        if ( p == NULL )
        {
            fprintf( stderr, "Unable to find student number!\n" );
            exit( EXIT_FAILURE );
        }

        //attempt to copy student number to struct
        if ( snprintf( si.studentNumber, sizeof si.studentNumber, "%s", p ) >= (int)(sizeof si.studentNumber) )
        {
            fprintf( stderr, "Not enough space to copy student number.\n" );
            exit( EXIT_FAILURE );
        }

        //attempt to read student name
        p = strtok( NULL, ";" );
        if ( p == NULL )
        {
            fprintf( stderr, "Unable to find student name!\n" );
            exit( EXIT_FAILURE );
        }

        //attempt to copy student name to struct
        if ( snprintf( si.studentName, sizeof si.studentName, "%s", p ) >= (int)(sizeof si.studentName) )
        {
            fprintf( stderr, "Not enough space to copy student name.\n" );
            exit( EXIT_FAILURE );
        }

        //attempt to read department
        p = strtok( NULL, ";" );
        if ( p == NULL )
        {
            fprintf( stderr, "Unable to find department!\n" );
            exit( EXIT_FAILURE );
        }

        //attempt to copy department to struct
        if ( snprintf( si.department, sizeof si.department, "%s", p ) >= (int)(sizeof si.department) )
        {
            fprintf( stderr, "Not enough space to copy department.\n" );
            exit( EXIT_FAILURE );
        }

        //attempt to read unknown field
        p = strtok( NULL, ";" );
        if ( p == NULL )
        {
            fprintf( stderr, "Unable to find unknown field!\n" );
            exit( EXIT_FAILURE );
        }

        //attempt to copy unknown field to struct
        if ( snprintf( si.unknown, sizeof si.unknown, "%s", p ) >= (int)(sizeof si.unknown) )
        {
            fprintf( stderr, "Not enough space to copy unknown field.\n" );
            exit( EXIT_FAILURE );
        }

        //attempt to read email
        p = strtok( NULL, ";" );
        if ( p == NULL )
        {
            fprintf( stderr, "Unable to find email!\n" );
            exit( EXIT_FAILURE );
        }

        //attempt to copy email to struct
        if ( snprintf( si.eMail, sizeof si.eMail, "%s", p ) >= (int)(sizeof si.eMail) )
        {
            fprintf( stderr, "Not enough space to copy eMail.\n" );
            exit( EXIT_FAILURE );
        }

        //print data from struct
        printf(
            "Successfully read the following student entry:\n"
            "Number    : %s\n"
            "Name      : %s\n"
            "Department: %s\n"
            "Unknown   : %s\n"
            "E-Mail    : %s\n"
            "\n",
            si.studentNumber, si.studentName, si.department,
            si.unknown, si.eMail
        );
    }
}

由于您还没有回应我要求澄清输入字段中第四个字段的含义的要求，我只是简单地在stuct StudentInfo中将其标记为“未知”。

但是，当我运行这个程序时，我会收到以下错误消息：

代码语言：javascript
复制
Not enough space to copy department.

这是因为您对struct StudentInfo的定义包含以下行：

代码语言：javascript
复制
char department[20];

这意味着它只能存储19字符加上终止空字符。但是，在输入文件中，您有Computer Engineering，它是20字符long (21包括终止空字符)。因此，必须将数组的大小至少增加到21。

你也有同样的问题

代码语言：javascript
复制
char eMail[20];

此数组不足以存储字符串。

代码语言：javascript
复制
enur.yilmaz@tedu.edu.tr

因为它需要24个字符(包括终止字符)

在将两个数组的大小从20增加到30之后，程序就可以工作了。它将有以下输出：

代码语言：javascript
复制
Successfully read the following student entry:
Number    : 10000000000
Name      : EDA NUR   YILMAZ
Department: Computer Engineering
Unknown   : 4
E-Mail    : enur.yilmaz@tedu.edu.tr

Successfully read the following student entry:
Number    : 10000000010
Name      : FEYZA  NUR  DUMAN
Department: Computer Engineering
Unknown   : 2
E-Mail    : fnur.duman@tedu.edu.tr

Successfully read the following student entry:
Number    : 20000000010
Name      : GOKHAN  YAMAC
Department: Computer Engineering
Unknown   : 2
E-Mail    : gokhan.yamac@tedu.edu.tr

Successfully read the following student entry:
Number    : 30000000030
Name      : CEREN  AYDINLI
Department: Computer Engineering
Unknown   : 2
E-Mail    : ceren.aydinli@tedu.edu.tr

Successfully read the following student entry:
Number    : 30000000010
Name      : DURU  YAMAC
Department: Computer Engineering
Unknown   : 3
E-Mail    : duru.yamac@tedu.edu.tr

Successfully read the following student entry:
Number    : 40000000010
Name      : SEVIL TERZI
Department: Computer Engineering
Unknown   : 2
E-Mail    : sevil.terzi@tedu.edu.tr

Successfully read the following student entry:
Number    : 50000000010
Name      : EREN  AYDIN
Department: Computer Engineering
Unknown   : 2
E-Mail    : eren.aydin@tedu.edu.tr

Successfully read the following student entry:
Number    : 50000000020
Name      : YAMAC    YILMAZ
Department: Computer Engineering
Unknown   : 2
E-Mail    : yamac.yilmaz@tedu.edu.tr

Successfully read the following student entry:
Number    : 60000000020
Name      : EDANUR    YILMAZ
Department: Computer Engineering
Unknown   : 2
E-Mail    : edanur.yilmaz@tedu.edu.tr

Successfully read the following student entry:
Number    : 70000000010
Name      : GOKHAN YAMAC
Department: Computer Engineering
Unknown   : 2
E-Mail    : gokhan.yamac18@tedu.edu.tr

但是，这个解决方案不太好的一点是，它包含大量的代码重复。处理所有5个字段的代码几乎是相同的，所以最好统一此代码：

代码语言：javascript
复制
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct StudentInfo
{
    char studentNumber[20];
    char studentName[20];
    char department[30];
    char unknown[20];
    char eMail[30];
};

int main( void )
{
    FILE *fpInput;
    char line[400];
    struct StudentInfo si;

    struct field
    {
        char *p_str;
        size_t size;
    };

    //arrange fields in an array, so that it can be used in
    //a loop
    struct field fields[] = {
        { si.studentNumber, sizeof si.studentNumber },
        { si.studentName,   sizeof si.studentName },
        { si.department,    sizeof si.department },
        { si.unknown,       sizeof si.unknown },
        { si.eMail,         sizeof si.eMail }
    };

    //open input file
    fpInput = fopen( "input.txt", "r" );
    if ( fpInput == NULL )
    {
        fprintf( stderr, "Error opening file!\n" );
        exit( EXIT_FAILURE );
    }

    //ignore first line of input
    fgets( line, sizeof line, fpInput );

    //read one line of input per loop iteration
    while ( fgets( line, sizeof line, fpInput ) != NULL )
    {
        char *p;

        //attempt to find newline character
        p = strchr( line, '\n' );

        //make sure entire line was read, and remove newline
        //character if necessary
        if ( p == NULL )
        {
            //a missing newline character is ok on end-of-file
            if ( !feof(fpInput) )
            {
                fprintf( stderr, "Line too long for input buffer!\n" );
                exit( EXIT_FAILURE );
            }
        }
        else
        {
            //remove newline character from input
            *p = '\0';
        }

        p = strtok( line, ";" );

        for ( size_t i = 0; i < sizeof fields / sizeof *fields; i++ )
        {
            //verify that field exists
            if ( p == NULL )
            {
                fprintf( stderr, "Unable to find student number!\n" );
                exit( EXIT_FAILURE );
            }

            //attempt to copy field to struct
            if ( snprintf( fields[i].p_str, fields[i].size, "%s", p ) >= (int)(fields[i].size) )
            {
                fprintf( stderr, "Not enough space to copy field.\n" );
                exit( EXIT_FAILURE );
            }

            p = strtok( NULL, ";" );
        }

        //print data from struct
        printf(
            "Successfully read the following student entry:\n"
            "Number    : %s\n"
            "Name      : %s\n"
            "Department: %s\n"
            "Unknown   : %s\n"
            "E-Mail    : %s\n"
            "\n",
            si.studentNumber, si.studentName, si.department,
            si.unknown, si.eMail
        );
    }
}
票数 1
EN

Stack Overflow用户

发布于 2022-05-15 22:34:15

您的代码出现了许多问题：

  • char operationType[2];只能容纳一个字符(另一个是因为\0);
  • struct StudentInfo *studentInfo=(struct StudentInfo*) malloc(sizeof(struct StudentInfo));太不必要了，long;
  • while(!feof(firstFile))是always wrong;
  • You误用了，scanf;
  • You没有检查fopen的返回值，fread;
  • The格式的文件暗示它是带有头的csv。在您的示例中，fread不是将您的文件读入struct StudentInfo的正确方法。appropriate.

更多的是fgets

@Andreas Wenzel已经提供了a solution。下面是使用sscanf的另一个版本

首先，重新定义您的结构，这样就更有意义了：

代码语言：javascript
复制
struct StudentInfo {
    char studentNumber[12];
    char studentName[50];
    char department[50];
    int weired;  // What is this?
    char eMail[50];
};

其次，定义一个从输入流读取一行的函数：

代码语言：javascript
复制
char *read_line(char *line, size_t size, FILE *stream)
{
    if(!fgets(line, size, stream))
        return NULL;
    
    size_t npos = strcspn(line, "\n");
    line[npos] = '\0';
    return line;
}

然后将其与sscanf结合使用

代码语言：javascript
复制
int main(int argc, const char *argv[])
{
    const char *filename = "file.txt";
    
    FILE *file = fopen(filename, "r");
    if (!file) {
        fprintf(stderr, "Could not open file %s\n", filename);
        exit(EXIT_FAILURE);
    }
    
    char line[1024]; // 1KB should be large enough
    struct StudentInfo students[100];
    size_t nstudents = 0;
    
    // Read and discard the first line
    read_line(line, sizeof line, file);
    
    // Read the rest of the file
    for (size_t lineno = 0; read_line(line, sizeof line, file); ++lineno) {
        char studentNumber[12];
        char studentName[50];
        char department[50];
        int weired;
        char eMail[50];
        
        int ret = sscanf(line, " %11[^;\n];%49[^;\n];%49[^;\n];%d;%49[^;\n];", studentNumber, studentName, department, &weired, eMail);
        
        if (ret != 5) {
            printf("> [ERROR] on line %ld: expected %d fields, but only parsed %d\n", lineno, 5, ret);
            continue;
        }
        
        // Copy data to struct array only when parsing succeeded
        
        struct StudentInfo *st = &students[nstudents++];
        strncpy(st->studentNumber, studentNumber, sizeof(studentNumber));
        strncpy(st->studentName, studentName, sizeof(studentName));
        strncpy(st->department, department, sizeof(department));
        st->weired = weired;
        strncpy(st->eMail, eMail, sizeof(eMail));
        
        //printf("%s\n%s\n%s\n%d\n%s\n\n", studentNumber, studentName, department, weired, eMail);
    }
    
    fclose(file);
    
    for (size_t i = 0; i < nstudents; ++i) {
        struct StudentInfo *st = &students[i];
        printf("Student #%ld\n", i+1);
        printf("%s\n%s\n%s\n%d\n%s\n\n", st->studentNumber, st->studentName, st->department, st->weired, st->eMail);
    }
}

在这里，%11[^;\n];部分的意思是“读取所有内容，直到找到换行符或分号，或者达到11个字符的最大限制，然后读取分号。”

输出：

代码语言：javascript
复制
Student #1
10000000000
EDA NUR   YILMAZ
Computer Engineering
4
enur.yilmaz@tedu.edu.tr

Student #2
10000000010
FEYZA  NUR  DUMAN
Computer Engineering
2
fnur.duman@tedu.edu.tr

Student #3
20000000010
GOKHAN  YAMAC
Computer Engineering
2
gokhan.yamac@tedu.edu.tr

Student #4
30000000030
CEREN  AYDINLI
Computer Engineering
2
ceren.aydinli@tedu.edu.tr

Student #5
30000000010
DURU  YAMAC
Computer Engineering
3
duru.yamac@tedu.edu.tr

Student #6
40000000010
SEVIL TERZI
Computer Engineering
2
sevil.terzi@tedu.edu.tr

Student #7
50000000010
EREN  AYDIN
Computer Engineering
2
eren.aydin@tedu.edu.tr

Student #8
50000000020
YAMAC    YILMAZ
Computer Engineering
2
yamac.yilmaz@tedu.edu.tr

Student #9
60000000020
EDANUR    YILMAZ
Computer Engineering
2
edanur.yilmaz@tedu.edu.tr

Student #10
70000000010
GOKHAN YAMAC
Computer Engineering
2
gokhan.yamac18@tedu.edu.tr
票数 0
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/72249036

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