Sox - Using silence effect in C++

Question

I am trying to use the sox silence effect in C++

char* silenceOptions[25];
silenceOptions[0] = "-l 1 0.2 1% -1 0.2 1%";
sox_effect_options(effect, 7, silenceOptions);

I get the output:

silence: usage: [ -l ] above_periods [ duration threshold[d|%] ] [ below_periods duration threshold[d|%] ]

What is the correct way of passing the arguments to the silence effect?

int sox_effect_options(sox_effect_t *effp, int argc, char * const argv[]);

I am confused whether argc is a number of arguments of the size of argv?
What wrong with "-l 1 0.2 1% -1 0.2 1%"?