前几日工作中有以科学计数法输出的需要，当时不知道库函数就有对应的格式，还自己写了一个，昨日经理说库函数自带，发现库函数的确支持。
linux执行man 3 printf，可以在手册中看到如下描述
e, E
The double argument is rounded and converted in the style [-]d.ddde±dd where there is one digit before the decimal-point character and the number of digits after it is equal to the precision; if the precision is missing, it is taken as 6; if the precision is zero, no decimal-point character appears. An E conversion uses the letter E (rather than e) to introduce the exponent. The exponent always contains at least two digits; if the value is zero, the exponent is 00.
实验代码如下：
#include<stdio.h>
int main(){
printf("%.2E\n", 0.00001);
printf("%.2E\n", 1.00001);
printf("%.2E\n\n", 1234.234);
printf("%.2e\n", 0.00001);
printf("%.2e\n", 1.00001);
printf("%.2e\n", 1234.234);
return 0;
}
1.00E-05
1.00E+00
1.23E+03
1.00e-05
1.00e+00
1.23e+03
sprintf也支持科学计数法的格式化，用法和printf相同。
