将制表符分隔文件读取到C中的结构

Question

I have a file with tab delimited data. I want to read the every line into a Structure. I have a code to read the data to char buffer. But I want to load the data into a Structure.

This is My sample data.

empname1\\t001\\t35\\tcity1

empname2\\t002\\t35\\tcity2

My Structure definition .

struct employee
{
  char *empname;
  char *empid;
  int age;
  char *addr;

};

My sample program to read data to a char array buffer

char buffer[BUF_SIZE];      /* Character buffer */
    input_fd = open (fSource, O_RDONLY);
    if (input_fd == -1) {
       perror ("open");
        return 2;
    }

    while((ret_in = read (input_fd, &buffer, BUF_SIZE)) > 0){

         // Do Some Process 
    }

Here I want to load the content to a structure variable instead of the character buffer. How I can achieve that?

Answer 1

Well, a possible solution could be

1. Read a complete line from the file using fgets() .

2. tokenize the input buffer based on the required delimiter [ tab in your case] using strtok() .

3. allocate memory ( malloc() / realloc() ) to a pointer variable of your structure.

4. copy the tokenized inputs into the member variables.

^{Note: 1. fgets() reads and stores the trailing \\n . 2. Please check carefully how to use strtok() . The input string should be mutable. 3. Allocate memory to pointers before using them. IMO, use statically allocated array as struct employee member variables.}

Answer 2

You can use the fscanf function. Open a file as a stream then use the fscanf to get a input from the file.

int fscanf(FILE *stream, const char *format, ...);
FILE *fp=fopen(fsource,"r+");
struct employee detail;
fscanf(fp,"%s %s %d %s",detail.empname,detail.empid,&detail.age,detail.addr);

Make sure that allocation of memory to the variables.

Or else you can use the strtok function. That time you have to use the sscanf function.

Answer 3

You can use fscanf to read each line from file, strtok to tokenize the line read.
Since your structure members are pointers, allocate memory appropriately.

The following minimal code does exactly what you want.

#define SIZE 50 
FILE *fp = NULL;                                                            
int i = 0;                                                                  
struct employee var = {NULL, NULL, 0, NULL};                                
char line[SIZE] = {0}, *ptr = NULL;   

/* 1. Open file for Reading */                                                 
if (NULL == (fp = fopen("file.txt","r")))                                   
{                                                                           
    perror("Error while opening the file.\n");                              
    exit(EXIT_FAILURE);                                                     
}

---

/* 2. Allocate Memory */                                                       
var.empname = malloc(SIZE);                                                 
var.empid = malloc(SIZE);                                                   
var.addr = malloc(SIZE); 

---

/* 3. Read each line from the file */   
while (EOF != fscanf(fp, "%s", line))                                       
{                                                                           
    /* 4. Tokenise the read line, using "\" delimiter*/                     
    ptr = strtok(line, "\\");                                                                                   
    var.empname = ptr;                                                      

    while (NULL != (ptr = strtok(NULL, "\\")))                              
    {                                                                       
        i++;                                                                

        /* 5. Store the tokens as per structure members , where (i==0) is first member and so on.. */
        if(i == 1)                                                          
            var.empid = ptr;                                                
        else if(i == 2)                                                     
            var.age = atoi(ptr);                                            
        else if (i == 3)                                                    
            var.addr = ptr;                                                 
    }                                                                       

    i = 0;        /* Reset value of i */                                                          
    printf("After Reading: Name:[%s] Id:[%s] Age:[%d] Addr:[%s]\n", var.empname, var.empid, var.age, var.addr);
}                                                                           

Working Demo: http://ideone.com/Kp9mzN

Few things to Note here:

1. This is guaranteed to work, as long as your structure definition (and order of members) remains the same (see manipulation of value i ).
2. strtok(line, "\\\\"); , Second argument is just escaping (first \\ ) the actual \\ character.

---

Clarification from the OP:

In your structure definition, third member is an int , however you're trying to read t35 into it (which is a string ).
So var.age = atoi(ptr); will give you 0 ,

You could change the structure definition, making third member as char * and allocating memory like other members.

Or change file contents, making sure an int is present as the third value.

Answer 4

I think this may be what you are looking for

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <unistd.h>
#include <fcntl.h>

#include <sys/stat.h>

struct employee
{
char *empname;
char *empid;
int age;
char *addr;

};

int readEmploee(char *line, struct employee *employee)
{
    char *token;
    char *saveptr;
    char *endptr;

    if ((employee == NULL) || (line == NULL))
        return 0;

    token = strtok_r(line, "\t", &saveptr);
    if (token == NULL)
        return 0;
    employee->empname = strdup(token);

    token = strtok_r(NULL, "\t", &saveptr);
    if (token == NULL)
        return 0;
    employee->empid = strdup(token);

    token = strtok_r(NULL, "\t", &saveptr);
    if (token == NULL)
        return 0;
    employee->age = strtol(token, &endptr, 10);
    if (*endptr != '\0')
        return 0;

    token = strtok_r(NULL, "\t", &saveptr);
    if (token == NULL)
        return 0;
    employee->addr = strdup(token);

    return 1;
}

char *mygetline(int fd)
{
    char  *line;
    size_t length;
    size_t count;
    char   character;

    line = malloc(128);
    if (line == NULL)
        return NULL;
    length = 0;
    count  = 1;
    do
    {
        if (read(fd, &character, 1) != 1) /* end of file probably reached */
        {
            free(line);
            return NULL;
        }
        else if (character != '\n')
        {
            if (length > 128 * count)
            {
                char *temp;
                temp = realloc(line, 128 * count);
                if (temp == NULL)
                {
                    free(line);
                    return NULL;
                }
                line   = temp;
                count += 1;
            }
            line[length++] = character;
        }
    } while (character != '\n');
    line[length] = 0;

    return line;
}

struct employee *readFile(const char *const fSource, size_t *count)
{
    struct employee *employees;
    int              employeeCount;
    int              input_fd;
    char            *line;

    if ((count == NULL) || (fSource == NULL))
        return NULL;

    *count        = 0;
    employees     = NULL;
    employeeCount = 0;
    input_fd      = open (fSource, O_RDONLY);
    if (input_fd == -1)
    {
        perror ("open");
        return NULL;
    }

    while ((line = mygetline(input_fd)) != NULL)
    {
        struct employee employee;
        if (readEmploee(line, &employee) != 0)
        {
            struct employee *temp;

            temp = realloc(employees, (1 + employeeCount) * sizeof(struct employee));
            if (temp != NULL)
                employees = temp;
            employees[employeeCount++] = employee;
        }
        free(line);
    }
    *count = employeeCount;

    return employees;
}

int
main()
{
    size_t           count;
    size_t           index;
    struct employee *employees;

    employees = readFile("somesamplefile.txt", &count);
    if (employees == NULL)
        return 1;
    for (index = 0 ; index < count ; index++)
    {
        struct employee current;

        current = employees[index];

        fprintf(stderr, "%s, %s, %d, %s\n", current.empname, current.empid, current.age, current.addr);
        if (current.empname != NULL)
            free(current.empname);
        if (current.empid != NULL)
            free(current.empid);
        if (current.addr != NULL)
            free(current.addr);
    }
    free(employees);
    return 0;
}