Thread: How to save array to file

There is a simple C-code, where I defined array of string type. Need to save it into ASCII-file (later I will need to read array back from this file). I know that I did something wrong in 'fwrite'. Please help me to find the problem and fix it.

Code:

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


char* a[2]      = {"130123456789", "2"};


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

    printf("\n a[0] = %s", a[0]);
    printf("\n a[1] = %s", a[1]);


// ====================================================

    FILE *file_01;

    if((file_01   = fopen("OUT_a.txt","w"))==NULL) {
        printf("CANNOT OPEN FILE OUT_a.txt 'w'\n");
        exit(1);
    };


    printf("\n strlen(a[0]) = %i", strlen(a[0]));
    printf("\n strlen(a[1]) = %i", strlen(a[1]));


    int t1 = fwrite(*a, (strlen(a[0])+strlen(a[1])), 1, file_01);

    printf("\n t1 = %i", t1);

    fclose(file_01);

// ====================================================

    printf("\n\nFINISH!\n");

    return 0;
}

Originally Posted by john.c

a is an array of two pointers and you are writing 13 bytes starting at the first pointer. If the pointers are 8 bytes each, you are writing the first 13 bytes of the pointer values. If they are 4 byte pointers then you are writing all 8 bytes of the two pointers plus 5 bytes of whatever happens to be directly after them in memory. You are not writing the strings at all (unless you have 4-byte pointers and part of the strings are in those 5 extra bytes).

Normally you don't use fwrite to write to a text file. fprintf is more usual.

Code:

fprintf(file_01, "%s\n%s\n", a[0], a[1]);

I found the following example in the internet:

Code:

int main()
{
    std::string array[] = { "S1", "S2", "S3" };
    std::cout << "A number of elements in array is: "
              << sizeof(array)/sizeof(array[0]) << '\n';
    foo(array);
}

The most interesting to me is the following line:

Code:

string array[] = { "S1", "S2", "S3" };

I tried to use 'string array[]...', but my compiler DevC++ didn't accept it. Maybe you know why?

Originally Posted by john.c

a is an array of two pointers and you are writing 13 bytes starting at the first pointer. If the pointers are 8 bytes each, you are writing the first 13 bytes of the pointer values. If they are 4 byte pointers then you are writing all 8 bytes of the two pointers plus 5 bytes of whatever happens to be directly after them in memory. You are not writing the strings at all (unless you have 4-byte pointers and part of the strings are in those 5 extra bytes).

Normally you don't use fwrite to write to a text file. fprintf is more usual.

Code:

fprintf(file_01, "%s\n%s\n", a[0], a[1]);

Somebody helped me with this code, now saving array to file works. I added second part - read array from file - compiler complained that something is wrong. Maybe you know where is mistake?

Code:

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


char* a[2]                   = {"0123456789", "2"};


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

    FILE *file_01;

    if((file_01               = fopen("OUT_a.txt","w"))==NULL) {
        printf("CANNOT OPEN FILE OUT_a.txt 'w'\n");
        exit(1);
    };


    for (size_t i=0; i<(sizeof(a)/sizeof(a[0])); i++) {
      fwrite(a[i], 1, strlen(a[i]) + 1, file_01);
    }


    fclose(file_01);
// ====================================================

 
 
// ====================================================
 
    if((file_01               = fopen("OUT_a.txt","r"))==NULL) {
        printf("CANNOT OPEN FILE OUT_a.txt 'r'\n");
        exit(1);
    };
 
 
    int  x0                   = sizeof(a)/sizeof(a[0]);
    char* b[x0];
 
 
    printf("\n");
    printf("\n (sizeof(b)/sizeof(b[0]))    = %i", (sizeof(b)/sizeof(b[0])) );            // [bytes]
 
 
    int i2                    = 0;
 
    while(fscanf(b[i2], "%s", file_01) != EOF) {
        printf("\n%s", b[i2]);
        i2++;
    }
 

 
    fclose(file_01);
// ====================================================
 

    printf("\n\nFINISH!\n");
 
 
    return 0;
}

Originally Posted by laserlight

Don't do this:..

Thank you for your reply!
Unfortunately I didn't get an email notification, so I read it just now.
I will modify the code based on your suggestions.