CODEWITHSUNDEEP
cstringprintf
Dumbo
Dumbo

Reputation: 14112

Building formatted strings in C

Lets say I have lots of printf usage, but I want to store them in a string and print them all in one go. Imagine the case below:

printf("%d,", _counter);
printf("IS REAL,", _condition);
printf("%f,", _value);
printf("%d,\r\n", _time);

What I want to do is to build a string and use printf only once when I am sure that I want to print it on screen. For example the output of above code will be:

1,IS REAL,663,1044

In C# I would use StringBuilder....but how to do this in C?

Upvotes: 3

Views: 8742

Answers (4)

unwind
unwind

Reputation: 399833

You use sprintf(), or (much better) snprintf().

char buffer[32];

snprintf(buffer, sizeof buffer, "%d,IS REAL,%f,%d\r\n", _counter, _value, _time);
printf("%s", buffer);

I skipped the _condition variable access, since that line didn't do any formatting.

Upvotes: 8

perreal
perreal

Reputation: 97948

As suggested, sprintf is what you are asking I believe, however, you can always do this:

printf("%d, IS REAL(%d), %f, %d,\r\n", _counter, _condition, _value,  _time);

and sprintf returns the number of characters written so you can use it like so:

#include <stdio.h>
#include <string.h>
int main() {
    char buf[256];
    int s = sprintf(buf, "This %d,", 12);
    s += sprintf(buf+s, "and this %f.", 1.0);
    s += sprintf(buf+s, ",also  %f", 2.0);
    printf("%s\n", buf);
    return 0;
}

Upvotes: 3

Devolus
Devolus

Reputation: 22084

To answer your qeustion, you can add as many formatters or strings as you want. 

printf("%d,IS REAL,%f,%d,\r\n", _counter, _value, _time);

Note, that I ommited this one:

printf("IS REAL,", _condition);

because you are goiving it as an argument, but didn't specify a format for it, just plain text, so it would be wrong. If you want to print _condition as value, then you must add also a format specifier like %d or whatever _condition is. If it is a boolean you could do something like this:

printf(""%s,",  (_condition == 1) ? "IS REAL" : "IS NOT");

But I don't know your code, so this is just a suggestion assuming you want something like this done.

If you want to build a string in memory, collecting all the data first, you have to use s(n)printf, but then you must make sure to allocate and deallocate enough space for your string.

Upvotes: 1

vdegenne
vdegenne

Reputation: 13270

create a function that takes the current string and the chunk that you want to plug on as arguments,

then malloc a new pointer on char with a length equal to (strlen(string) + strlen(chunk) + 1)

you can use sprintf let say:

sprintf(newstring, "%s%s", string, chunk);

then free the last two string if you allocate them manually.

Returns the pointer of the new string.

Upvotes: 0

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