我在外部文件中用一个指针指向了一个内存，并赋值，但在主函数中调用时却莫名地被清零了，这是怎么回事？

我也不知道你想说什么回事


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LZ说得好深奥喔

楼主..具体点行么?
或者把代码贴出来也好啊..

外部变量在定义时如果没有赋值,默认值为0.跟局部变量不一样/.


我只能告诉你这些,
因为我没看懂你在说什么

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

int AADT=1992;   /*AADT*/
double avaxle=2.54;  /*axle number per truck*/
double lane=0.5;           /*lane coefficient*/
double direction=0.7;      /*direction coefficient*/

double PSIGLE=57.1;
double PTRADEM=34.5;
double PTRIDEM=8.4;  /*Traffic composition*/



double distribution[100];

int section;

void main()
{
 int i,j,k,l,month,day,hour;
 double temperature=0.0;  /* for read the everyday temperature*/
 
 double yeartraffic; /* total year traffic*/

 double ptemperature;
 double ns,nr;

 double h; /* pavement thickness*/
 double z; /* half pavement thickness*/
 double modulus,strain;
 double c=0.435373; /* fatigue function*/

 double d,damage; /*cumulative damage*/
 double n,nn; /* Miner hypothisis*/
 double monthadjust[12]; /*for read the month traffic adjust coefficient*/
 double houradjust[24];  /*for read the day traffic adjust coefficient */

double singleweight[50],singlepercent[50];
double trademweight[50],tradempercent[50];
double tridemweight[50],tridempercent[50];

 int days; /*month days*/

 int SN=0,TAN=0,TIN=0;
 

 FILE *ft;
 FILE *fp;
 FILE *fs;
 FILE *fr;

 printf("Please input pavement structure number(1,2,3,4,5):\n");
 scanf("%d",&section);
 if(section==1) h=50;
 if(section==2) h=38;
 if(section==3) h=38;
 if(section==4) h=33;
 if(section==5) h=15;
 z=h/2;
 yeartraffic=AADT*avaxle*365*lane*direction; /*year total traffic*/

 fs=fopen("month.txt","r");
 if(fs==NULL)printf("file open error!\n");
 while(!feof(fs))
 {fscanf(fs,"%d %lf\n",&i,&ns);
  monthadjust[i]=ns;
  printf("month=%d,coefficient=%f\n",i,monthadjust[i]);
  }
  fclose(fs);
  system("pause"); /* to read the month traffic adjust coefficient*/

printf("month=%f\n",monthadjust[12]);system("pause");
 fs=fopen("hour.txt","r");
 if(fs==NULL) printf("file open errors!\n");
 while(!feof(fs))
  {fscanf(fs,"%d %lf\n",&i,&ns);
   houradjust[i]=ns;
   printf("hour=%d,coefficient=%f\n",i,houradjust[i]);
   }
   fclose(fs);
   system("pause"); /*to read the day traffic adjust coefficient*/
   printf("month=%f\n",monthadjust[12]);system("pause");
   for(i=1;i<=12;i++)
   printf("%f\n",monthadjust[i]);

}
monthadjust[i]变量当i＝12时被没名奇妙的变为houradjust[i]一样的数是怎么回事？
c中的变量还会冲突或自动改变吗？

c语言变量莫名其妙被改变
#include<stdio.h>
#include<math.h>

int AADT=1992;   /*AADT*/
double avaxle=2.54;  /*axle number per truck*/
double lane=0.5;           /*lane coefficient*/
double direction=0.7;      /*direction coefficient*/

double PSIGLE=57.1;
double PTRADEM=34.5;
double PTRIDEM=8.4;  /*Traffic composition*/



double distribution[100];

int section;

void main()
{
int i,j,k,l,month,day,hour;
double temperature=0.0;  /* for read the everyday temperature*/

double yeartraffic; /* total year traffic*/

double ptemperature;
double ns,nr;

double h; /* pavement thickness*/
double z; /* half pavement thickness*/
double modulus,strain;
double c=0.435373; /* fatigue function*/

double d,damage; /*cumulative damage*/
double n,nn; /* Miner hypothisis*/
double monthadjust[12]; /*for read the month traffic adjust coefficient*/
double houradjust[24];  /*for read the day traffic adjust coefficient */

double singleweight[50],singlepercent[50];
double trademweight[50],tradempercent[50];
double tridemweight[50],tridempercent[50];

int days; /*month days*/

int SN=0,TAN=0,TIN=0;


FILE *ft;
FILE *fp;
FILE *fs;
FILE *fr;

printf("Please input pavement structure number(1,2,3,4,5):\n");
scanf("%d",&section);
if(section==1) h=50;
if(section==2) h=38;
if(section==3) h=38;
if(section==4) h=33;
if(section==5) h=15;
z=h/2;
yeartraffic=AADT*avaxle*365*lane*direction; /*year total traffic*/

fs=fopen("month.txt","r");
if(fs==NULL)printf("file open error!\n");
while(!feof(fs))
{fscanf(fs,"%d %lf\n",&i,&ns);
  monthadjust[i]=ns;
  printf("month=%d,coefficient=%f\n",i,monthadjust[i]);
  }
  fclose(fs);
  system("pause"); /* to read the month traffic adjust coefficient*/

printf("month=%f\n",monthadjust[12]);system("pause");
fs=fopen("hour.txt","r");
if(fs==NULL) printf("file open errors!\n");
while(!feof(fs))
  {fscanf(fs,"%d %lf\n",&i,&ns);
   houradjust[i]=ns;
   printf("hour=%d,coefficient=%f\n",i,houradjust[i]);
   }
   fclose(fs);
   system("pause"); /*to read the day traffic adjust coefficient*/
   printf("month=%f\n",monthadjust[12]);system("pause");
   for(i=1;i<=12;i++)
   printf("%f\n",monthadjust[i]);

}
monthadjust[i]变量当i＝12时被没名奇妙的变为houradjust[i]一样的数是怎么回事？
c中的变量还会冲突或自动改变吗？

printf("month=%f\n",monthadjust[12]);

monthajust只有0~11这12个元素，你引用12干嘛？

0-11为合法下标。12越界，至于为什么会和别的一样，与数据存储的细节有关。