Question

请考虑以下代码：

#include <stdio.h>
#include <math.h>

#define INFTY 1000.0
#define EPS 0.0001
#define XRANGE 2
#define URANGE 2

float absf(float);
float E(float,float,float,float,float,float);

int main(){
    FILE* out;
    float T,R,G,ALPHA,STEP,x,u;
    char filename [45];
    int c;
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("Enter the dimensionless parameters greater or equal to 0:\nT = ");
    scanf("%f",&T);
    do { c=getchar(); } while ( c != '\n');//flush stdin
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("R = ");
    scanf("%f",&R);
    do { c=getchar(); } while ( c != '\n');
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("G = ");
    scanf("%f",&G);
    do { c=getchar(); } while ( c != '\n');
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("alpha = ");
    scanf("%f",&ALPHA);
    do { c=getchar(); } while ( c != '\n');
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("step size (recommended:0.001 to 0.01): ");
    scanf("&f",&STEP);
    do { c=getchar(); } while ( c != '\n');
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    if((T<0)||(R<0)||(G<0)||(ALPHA<0)||(STEP<0)) return 1;//crash if <0
    sprintf(filename,"%.4g_%.4g_%.4g_%.4g_%.5g.dat",T,R,G,ALPHA,STEP);
    out = fopen(filename,"w");
    fprintf(out,"#T=%.3e R=%.3e G=%.3e alpha=%.3e\n",T,R,G,ALPHA);
    //do the job
    fclose(out);
    return 0;
}

这里的问题是它似乎完全忽略了应该输入步长的最后scanf();它只需要记忆中的任何垃圾并与它一起使用，通常只是一个非常小的数字。这个输出很有特色：

0.000000 0.000000 0.000000 0.000000 72406190763540480.000000
Enter the dimensionless parameters greater or equal to 0:
T = 1
1.000000 0.000000 0.000000 0.000000 72406190763540480.000000
R = 1
1.000000 1.000000 0.000000 0.000000 72406190763540480.000000
G = 1
1.000000 1.000000 1.000000 0.000000 72406190763540480.000000
alpha = 1.2
1.000000 1.000000 1.000000 1.200000 72406190763540480.000000
step size (recommended:0.001 to 0.01): 0.01
1.000000 1.000000 1.000000 1.200000 72406190763540480.000000

很明显，除了最后一个变量之外，还可以覆盖每个变量。甚至在最后scanf()完成之前就创建了该文件。将步长输入移到顶部会产生另一个问题：

step size (recommended:0.001 to 0.01): 0.01
Enter the dimensionless parameters greater or equal to 0:
T = R = 1
G = 1
alpha = 1.2
^C

在这种情况下，STEP实际上并未被0.01覆盖，但仍然是一个非常小的数字。我已经查找了类似的案例，但似乎没有任何广泛的问题，如输入中的流氓空格。我按照建议here stdin后scanf()正在刷新{。}}。

我期待着任何建议。提前谢谢。

Answer 1

您使用了＆＃39;＆amp;＆＃39;代替＆＃39;％＆＃39;在scanf中（＆＃34;＆amp; f＆＃34;，＆amp; STEP）;

#include <stdio.h>
#include <math.h>

#define INFTY 1000.0
#define EPS 0.0001
#define XRANGE 2
#define URANGE 2

float absf(float);
float E(float,float,float,float,float,float);

int main(){
    FILE* out;
    float T,R,G,ALPHA,STEP,x,u;
    char filename [45];
    int c;
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("Enter the dimensionless parameters greater or equal to 0:\nT = ");
    scanf("%f",&T);
    do { c=getchar(); } while ( c != '\n');//flush stdin
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("R = ");
    scanf("%f",&R);
    do { c=getchar(); } while ( c != '\n');
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("G = ");
    scanf("%f",&G);
    do { c=getchar(); } while ( c != '\n');
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("alpha = ");
    scanf("%f",&ALPHA);
    do { c=getchar(); } while ( c != '\n');
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    printf("step size (recommended:0.001 to 0.01): ");

用％f替换＆amp; f，它将起作用的scanf（＆＃34;＆安培; F＆＃34;，＆安培; STEP）;

    do { c=getchar(); } while ( c != '\n');
    printf("%f %f %f %f %f\n",T,R,G,ALPHA,STEP);//debug
    if((T<0)||(R<0)||(G<0)||(ALPHA<0)||(STEP<0)) return 1;//crash if <0
    sprintf(filename,"%.4g_%.4g_%.4g_%.4g_%.5g.dat",T,R,G,ALPHA,STEP);
    out = fopen(filename,"w");
    fprintf(out,"#T=%.3e R=%.3e G=%.3e alpha=%.3e\n",T,R,G,ALPHA);
    //do the job
    fclose(out);
    return 0;
}

最后一次scanf（）被跳过或被忽略

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