CODEWITHSUNDEEP
cstringprintfcustomizationargs
drpytho
drpytho

Reputation: 125

Log data. Customize fprintf - C

I want to customize output to a file from my program.

void http_log(char* msg, ...)
{
    char* prePend = "Date-Time: %s === ";//Prepended text
    size_t len1 = strlen(prePend);
    size_t len2 = strlen(msg);
    char *s = malloc(len1 + len2 + 1);  //The new string
    memcpy(s, prePend, len1);
    memcpy(s + len1, msg, len2 + 1); // includes terminating null

    time_t rawtime;
    struct tm * timeinfo;
    time ( &rawtime );
    timeinfo = localtime ( &rawtime );

    char *dateTime = asctime (timeinfo);//Get the current date time
    dateTime[strlen(dateTime) - 1] = 0;//Take away the new line character 

    va_list args;
    va_start( args, msg);

    //I think the problem lies here... 
    fprintf( log_fd, s, dateTime, args);//Print it to the log file. log_fd is already created and opened.
    printf(s, dateTime, args);//Prints to screen. 

    va_end( args);
    free( s);
}

I want to add some standard text before the output from http_log(); (The current date in this case). After that i want to add some customizable text that you pass in to the http_log function http_log("This will be appended after the date \n");. and at last i want to be able to use the %s, %d, %ld and so on (Don't know what they are called) like http_log("Connected with IP address %s\n", IP_addres);

My problem is that the values i pass through does not get printed. Should i try to combine the string with the values before i combine the values or... Or is there some other other thing that is wrong with my code??

I'm grateful for all the help && || *pointers

Some C fun :)

Upvotes: 1

Views: 503

Answers (2)

Martin R
Martin R

Reputation: 540065

You cannot pass the va_list args to printf(), but to vprintf(). And you cannot combine an "additional argument" dateTime with the va_list, so you have to print them separately:

void http_log(char* msg, ...)
{
    char *dateTime = ...;
    fprintf(log_fd, "Date-Time: %s === ", dateTime);
    printf("Date-Time: %s === ", dateTime);

    va_list args;

    va_start(args, msg);
    vfprintf(log_fd, msg, args);
    va_end( args);

    va_start(args, msg);
    vprintf(msg, args);
    va_end( args);
}

Upvotes: 2

danadam
danadam

Reputation: 3450

I don't think it's possible with only one call to printf(). Your message and parameters you have to pass to v version of the print function, vfprintf() in your case. The date (or whatever you want to generate inside http_log()) you have to pass to non-v version of the print function.

Upvotes: 0

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