how to handle ints and strings when writing to file

**agentsmith** · 04-22-2008

Is it possible for one array to contain a string and few ints?? I want to write to a text file a string followed by a few ints, so they all appear on the same line in the file. Example of what I want to input:

Code:

string int int int \n

The only way I know to write stuff into a file is doing it one array at a time, using fputs, but my problem is that fputs only deals with strings. So my question is how can I write a mixture of strings and ints to a file one line at a time and what functions would I use. Also if such thing can be done, would it then be problematic to extract them ?

**brewbuck** · 04-22-2008

Originally Posted by agentsmith

Is it possible for one array to contain a string and few ints?? I want to write to a text file a string followed by a few ints, so they all appear on the same line in the file. Example of what I want to input:

Code:

string int int int \n

The only way I know to write stuff into a file is doing it one array at a time, using fputs, but my problem is that fputs only deals with strings. So my question is how can I write a mixture of strings and ints to a file one line at a time and what functions would I use. Also if such thing can be done, would it then be problematic to extract them ?

Code:

fprintf(file, "%s %d %d %d\n", the_string, val0, val1, val2);

Perhaps?

**agentsmith** · 04-22-2008

Thanks. Now once its in the file do I treat it as a string when retrieving it?

**brewbuck** · 04-22-2008

Originally Posted by agentsmith

Thanks. Now once its in the file do I treat it as a string when retrieving it?

Yes, it's a string once it passes through fprintf(). To convert back to string, int, int, int, you might be able to use fgets() followed by sscanf("%s %d %d %d") but there are caveats, namely if the string contains a space.

**maverix** · 04-23-2008

better still, you could declare a structure as per the requirements and write it to files

Code:

#define STR_SIZE 20

typedef struct {
    char string[STR_SIZE];
    int a;
    int b;
    int c;
}DATA;
FILE *fp;
DATA *item;

fp = fopen("filename.txt", "w+");
...
...
item = malloc(sizeof *item);
...
...
strcpy(item->string, "Hello");
item->a = 10;
item->b = 20;
item->c = 30;

fwrite(item,sizeof(*item),1,fp);
...
...
{
    DATA *temp;
    FILE *rfp;
    temp = malloc(sizeof *temp);

    rfp = fopen("filename.txt", "r");
    fread(temp,sizeof(*temp),1,rfp);
    printf("%s %d %d %d\n", temp->string, temp->a, temp->b, temp->c);
}
...
...

cheers
maverix

**Elysia** · 04-23-2008

It need not necessary by on the heap, however:

Code:

#define STR_SIZE 20

typedef struct {
    char string[STR_SIZE];
    int a;
    int b;
    int c;
}DATA;
FILE *fp;
DATA item;

fp = fopen("filename.txt", "w+");
...
...
...
...
strcpy(item.string, "Hello");
item.a = 10;
item.b = 20;
item.c = 30;

fwrite(&item,sizeof(item),1,fp);
...
...
{
    DATA temp;
    FILE *rfp;

    rfp = fopen("filename.txt", "r");
    fread(&temp,sizeof(temp),1,rfp);
    printf("%s %d %d %d\n", temp.string, temp.a, temp.b, temp.c);
}
...
...

This also solves your do not free memory case.

**matsp** · 04-23-2008

And those last two examples are creating a binary file, which is not always a good choice for saving data to a file - you can't for example use a text-editor to check it.

--
Mats

**Elysia** · 04-23-2008

That's linux talk. The Windows way is that config files are not supposed to be edited directly. The application should handle those.
Arguments against binary files is that it can break portability. A program that runs on OS X can't open config files created by the same program running under OS Y. Or the same logic with compiler X and compiler Y.
But binary files are the easiest way of creating files, at least in C.

**laserlight** · 04-23-2008

Arguments against binary files is that it can break portability. A program that runs on OS X can't open config files created by the same program running under OS Y. Or the same logic with compiler X and compiler Y.

That's true, though if say, the binary file was an SQLite database file, it would be consistent across platforms and examinable by any database viewing software that supports SQLite.

**Elysia** · 04-23-2008

Agreed, databases are generally recommended. SQLite, which is written in C, can replace the standard fopen with its own functionality.
It's a good thing since tie increases portability and makes it easier to manage complex files, registers, etc.
It's just a shame no one is teaching their students to use a small database instead of files

**matsp** · 04-23-2008

Originally Posted by Elysia

That's linux talk. The Windows way is that config files are not supposed to be edited directly.

But the simple fact that you can take a config file (or whatever the purpose of the file is).

Yes, I agree, creating binary files is simpler - but it also makes it harder to "look at" the content of the file without using some code that knows the format of the file. It's requires more effort to add further fields to the file (assuming the input function is flexible).

--
Mats

**Elysia** · 04-23-2008

All these problems would nearly be solved by using a database. Gotta love those small buggers, eh?

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