CODEWITHSUNDEEP
cprintf
user1373475
user1373475

Reputation: 33

How-to pass a function into fprintf

I have my function dumpArray(); which does this:

void dumpArray(void)
{
       while(p <= i)
       {
           printf("%i:", packet[p].source);
           printf("%i:", packet[p].dest);
           printf("%i:", packet[p].type);
           printf("%i\n", packet[p].port);
           p++;
       }
}

And I'm trying to pass this into a fprintf(); as such:

void fWrite(void)
{
    char fileName[30] = { '\0' };
    printf("Please specify a filename: ");
    scanf("%s", fileName) ;
    FILE *txtFile;
    txtFile = fopen(fileName, "w");
    if (txtFile == NULL)
    {
        printf("Can't open file!");
        exit(1);
    }
    else fprintf(txtFile, dumpArray());
}

I'm trying to write the result of dumpArray(); into the file.
Could anyone see where I'm going wrong and point me in the right direction.

Upvotes: 1

Views: 1484

Answers (4)

CherryQu
CherryQu

Reputation: 3393

The function declaration of fprintf states that it want some char* argument but dumpArray() is not returning a char*.

int fprintf ( FILE * stream, const char * format, ... );

If you want write to file in the dumpArray(), you can pass txtFile to dumpArray() and do fprintf inside the function. Or you could first collect all data you want to write to the file in a buffer (such as a char[]) and then write it altogether.

For example:

void dumpArray(FILE * txtFile)
{
       while(p <= i)
       {
           fprintf(txtFile, packet[p].source);
           fprintf(txtFile, packet[p].dest);
           fprintf(txtFile, packet[p].type);
           fprintf(txtFile, packet[p].port);
           fprintf(txtFile, "\n");
         p++;
       }
}

void fWrite(void)
{
    char fileName[30] = { '\0' };
    printf("Please specify a filename: ");
    scanf("%s", fileName) ;
    FILE *txtFile;
    txtFile = fopen(fileName, "w");
    if (txtFile == NULL)
    {
        printf("Can't open file!");
        exit(1);
    }
    else dumpArray(txtFile);

Upvotes: 1

user1207456
user1207456

Reputation:

Your first function is dumping its output into stdout and returning nothing, so it just won't result in an output that fprintf can capture.

You'll need to figure out how long all of those printf strings are and allocate the appropriate amount of memory to sprintf it and then return the string.

Alternatively, you should pass a function pointer to dumpArray pointing at the printf-like function that will instead write to a file:

void printfLike(format, data) {
    fprintf(fileConst, format, data);
}

...

dumpArray(printfLike);

Something of that nature.

Upvotes: 2

Justin
Justin

Reputation: 2372

You could rewrite dumparray to either write to stdout or to your textfile depending which stream you pass in.

So you would change all of your printf calls to fprintf and pass the stream as the first argument.

Upvotes: 3

Ed Heal
Ed Heal

Reputation: 60037

Where do you start?

Plead look up the page for fprintf and printf.

Change dumpArray into reuturning a character array. WHat is p?

That is for starters - Re-read you text book on C and also manual pages on C

Upvotes: 0

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