21世纪C语言 第2章 调试，测试，文档
使用调试器
关于调试器的第一个简明提示：总是使用调试器。
一个调试侦探故事
调试代码：
#include <math.h>
#include <stdio.h> //size_t
typedef struct meanvar {double mean, var;} meanvar;
meanvar mean_and_var(const double *data){
long double avg = 0,
avg2 = 0;
long double ratio;
size_t count= 0;
for(size_t i=0; !isnan(data[i]); i++){
ratio = count/(count+1);
count ++;
avg *= ratio;
avg2 *= ratio;
avg += data[i]/(count +0.0);
avg2 += pow(data[i], 2)/(count +0.0);
}
return (meanvar){.mean = avg,
.var = avg2 - pow(avg, 2)}; //E[x^2] - E^2[x]
}
int main(){
double d[] = { 34124.75, 34124.48,
34124.90, 34125.31,
34125.05, 34124.98, NAN};
meanvar mv = mean_and_var(d);
printf("mean: %.10g var: %.10g\n", mv.mean, mv.var*6/5.);
double d2[] = { 4.75, 4.48,
4.90, 5.31,
5.05, 4.98, NAN};
mv = mean_and_var(d2);
mv.var *= 6./5;
printf("mean: %.10g var: %.10g\n", mv.mean, mv.var);
}使用CFLAGS="-g -Wall -std=gnu11 -O3" make stddev编译代码，gdb stddev_bugged调试代码。