E = exponent expression, simply means power(10, n) or 10 ^ n
F = fraction expression, default 6 digits precision
G = gerneral expression, somehow smart to show the number in a concise way (but really?)
See the below example,
The code
void main(int argc, char* argv[])
{
double a = 4.5;
printf("=>>>> below is the example for printf 4.5\n");
printf("%%e %e\n",a);
printf("%%f %f\n",a);
printf("%%g %g\n",a);
printf("%%E %E\n",a);
printf("%%F %F\n",a);
printf("%%G %G\n",a);
double b = 1.79e308;
printf("=>>>> below is the exbmple for printf 1.79*10^308\n");
printf("%%e %e\n",b);
printf("%%f %f\n",b);
printf("%%g %g\n",b);
printf("%%E %E\n",b);
printf("%%F %F\n",b);
printf("%%G %G\n",b);
double d = 2.25074e-308;
printf("=>>>> below is the example for printf 2.25074*10^-308\n");
printf("%%e %e\n",d);
printf("%%f %f\n",d);
printf("%%g %g\n",d);
printf("%%E %E\n",d);
printf("%%F %F\n",d);
printf("%%G %G\n",d);
}
The output
=>>>> below is the example for printf 4.5
%e 4.500000e+00
%f 4.500000
%g 4.5
%E 4.500000E+00
%F 4.500000
%G 4.5
=>>>> below is the exbmple for printf 1.79*10^308
%e 1.790000e+308
%f 178999999999999996376899522972626047077637637819240219954027593177370961667659291027329061638406108931437333529420935752785895444161234074984843178962619172326295244262722141766382622299223626438470088150218987997954747866198184686628013966119769261150988554952970462018533787926725176560021258785656871583744.000000
%g 1.79e+308
%E 1.790000E+308
%F 178999999999999996376899522972626047077637637819240219954027593177370961667659291027329061638406108931437333529420935752785895444161234074984843178962619172326295244262722141766382622299223626438470088150218987997954747866198184686628013966119769261150988554952970462018533787926725176560021258785656871583744.000000
%G 1.79E+308
=>>>> below is the example for printf 2.25074*10^-308
%e 2.250740e-308
%f 0.000000
%g 2.25074e-308
%E 2.250740E-308
%F 0.000000
%G 2.25074E-308