英文:
How do I use struct and arrays to fill a file using fwrite function in C?
问题
我想创建一个程序，使用**fwrite()**将5个学生的属性（学号，名，姓）填充到文件中，我尝试使用结构体和数组来解决这个问题，如下所示：
#include <stdio.h>int main(){struct Student{char* matricule;char* nom;char* prenom;};Student student[5]; // 这里应该是 student[5]，而不是 student[4]student[0].matricule = "m001";student[0].nom = "Boussaha";student[0].prenom = "Borhanedine";student[1].matricule = "m002";student[1].nom = "Toaba";student[1].prenom = "Anes";student[2].matricule = "m003";student[2].nom = "Laamari";student[2].prenom = "Loqmane";student[3].matricule = "m004";student[3].nom = "Dellachi";student[3].prenom = "Amir";student[4].matricule = "m005";student[4].nom = "Zenfour";student[4].prenom = "Abdelmouiz";FILE *f;f = fopen("list.data", "wb");for (int i = 0; i < 5; i++){fwrite(student[i].matricule, sizeof(char), strlen(student[i].matricule), f);fwrite(student[i].nom, sizeof(char), strlen(student[i].nom), f);fwrite(student[i].prenom, sizeof(char), strlen(student[i].prenom), f);}fclose(f); // 没有关闭文件流return 0; // 函数需要返回一个值}
我猜想并希望代码没有错误。当我调试程序时，文件被创建，但是我发现它是空的。我在想为什么文件是空的，而我期望文件中应该填充有每个学生的属性？
英文:
I want to create a program that fills a file with properties of 5 students ( matricule , firstname , lastname ) using fwrite(), i tried to solve that using struct with arrays as shown bellow :
#include<stdio.h>int main(){struct Student{char* matricule;char* nom ;char* prenom;};Student student[4];student[0].matricule = "m001";student[0].nom = "Boussaha";student[0].prenom = "Borhanedine";student[1].matricule = "m002";student[1].nom = "Toaba";student[1].prenom = "Anes";student[2].matricule = "m003";student[2].nom = "Laamari";student[2].prenom = "Loqmane";student[3].matricule = "m004";student[3].nom = "Dellachi";student[3].prenom = "Amir";student[4].matricule = "m005";student[4].nom = "Zenfour";student[4].prenom = "Abdelmouiz";FILE *f;f = fopen("list.data" , "wb");for (int i = 0; i < 5; i++){fwrite(student[i].matricule , sizeof(student[i].matricule) , 5 , f);fwrite(student[i].nom , sizeof(student[i].nom) , 5 , f);fwrite(student[i].prenom , sizeof(student[i].prenom) , 5 , f);}}
I guess and hope nothing is wrong in the code.
When I debug the program, the file gets created but I find it empty. I am wondering why it is empty when I was expecting the file to be filled with the properties of each student?
答案1
得分: 0
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Student student[4];分配了足够的空间用于 4 个元素。这意味着student[0]到student[3]是有效的，但student[4]是无效的。访问student[4]会导致程序行为不可预测。将其更改为Student student[5]。 -
f = fopen("list.data", "wb");是可以的，但你有检查错误吗？if (f == 0)表示发生了错误。小心总比抱歉好。 -
fwrite(student[i].XYZ, sizeof(student[i].XYZ), 5, f);是非常错误的。我不确定你是否是新手，但我可以告诉你sizeof不是你想象的那样工作的。而且我敢打赌你似乎不知道为什么有个5在那里。请将sizeof替换为strlen，并将5替换为1。
英文:
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Student student[4];allocates enough room for 4 elements. This meansstudent[0]throughstudent[3]is valid, butstudent[4]is not valid. Accessingstudent[4]effectively makes you program behave unpredictably. Set it toStudent student[5]. -
f = fopen("list.data" , "wb");is okay, but did you check for errors?if(f==0)then an error has occurred. Better safe than sorry. -
fwrite(student[i].XYZ , sizeof(student[i].XYZ) , 5 , f);is very wrong. I'm not sure if you're new to C but I can tell you thatsizeofdoes not do what you think it does. And I bet you don't seem to know why that5is there either. Replacesizeofwithstrlen, and replace5with1.
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