我可能需要你的帮助来解决这个问题...... 我正在学习C并找到问题，如何正确读取二进制文件。
我填充了一个struct数组，然后在二进制文件上写入并尝试读取它，但这并没有显示任何内容。
代码在pastebin中
#include <stdio.h>
#include <ctype.h>
#include <math.h>
typedef struct {
int id;
char name[100];
char document[14];
float testGrade;
} Candidate;
typedef struct {
int id;
float testGrade;
} Grade;
FILE * openFile(char filename[100], char filemode[3]) {
FILE *p = fopen(filename, filemode);
if (!p) {
printf("Error to open %s file. \nThe program will be closed.",filename);
exit(1);
}
}
void addCandidate(int newId, int numbersOfNewCandidate, char candidateFilename[100], char gradeFilename[100]) {
int counter = 0;
float testGrade = 0;
Candidate*candidate;
candidate= malloc(sizeof(Candidate) * numbersOfNewCandidate);
Grade *grade;
grade= malloc(sizeof(Grade) * numbersOfNewCandidate);
for(;counter< numbersOfNewCandidate; counter++) {
system("@cls||clear");
printf("Adding #%d:",newId);
printf("\n---------------\n");
printf("\nName of candidate: ");
gets(&candidate[counter].name);
printf("\nDocument: ");
gets(&candidate[counter].document);
do {
printf("\nTest grade (between 0 and 10): ");
scanf("%f",&testGrade);
printf("\n---------------\n");
if (testGrade < 0 || testGrade > 10) {
printf("\nERROR!\nTest grade %.2f invalid, please try again with a grade between 0 and 10.\n",testGrade);
}
} while(testGrade < 0 || testGrade > 10);
candidate[counter].id = newId;
grade[counter].id = newId;
candidate[counter].testGrade = testGrade;
grade[counter].testGrate = testGrade;
newId++;
fflush(stdin);
}
FILE *candidateFile = openFile(candidateFilename, "a+b");
fwrite(candidate, sizeof(candidate),numbersOfNewCandidate, candidateFile );
FILE *gradeFile = openFile(gradeFilename, "a+b");
fwrite(grade, sizeof(grade),numbersOfNewCandidate, gradeFile );
fclose(candidateFile);
fclose(gradeFile);
free(candidate);
free(grade);
}
void showCandidate(int typeOfSearch, char valueToSearch[100]) {}
void listAllCandidates(char candid[100]) {
FILE *fp = openFile(candidateFilename, "rb");
//fseek(fp,0,SEEK_SET);
Candidate *candidate = NULL;
candidate = malloc(sizeof(Candidate) + 1);
while(fread(&candidate,sizeof(Candidate),1,fp) == 1) {
printf("\n\nId: %d \nName: %s \nDocument: %s \nGrade: %.2f",candidate->id,candidate->name,candidate->document, candidate->testGrade);
}
getche();
free(candidate);
}
void main(){
int lastId = 0;
char candidateFilename[100] = "candidates.bin";
char gradeFilename[100] = "classificationList.bin";
char option;
do {
system("@cls||clear");
printf("Menu: \n");
printf("1 - Add candidates \n");
// printf("2 - Search by name \n");
// printf("3 - Search by document \n");
// printf("---------------------------\n");
// printf("4 - Show Max Grade, Minimum, Avg \n");
printf("5 - List candidates \n");
printf("6 - Erase files \n");
printf("---------------------------\n");
printf("S - Exit \n");
printf("\n\n");
option = toupper(getche());
switch(option) {
case '1':
system("@cls||clear");
int numbersOfNewCandidate = 0;
int newId = 0;
printf("Home > Add candidates\n\n");
printf("Please give the number of new candidates: ");
scanf("%d",&numbersOfNewCandidate);
newId = lastId;
lastId += numbersOfNewCandidate;
fflush(stdin);
addCandidate(newId + 1, numbersOfNewCandidate, candidateFilename, gradeFilename);
printf("\n\nAdding new candidates: Finished \n");
break;
// case '2':
// printf("\noption %c@\n",option);
// break;
// case '3':
// printf("\noption %c#\n",option);
// break;
// case '4':
// printf("\noption %c?\n",option);
// break;
case '5':
listAllCandidates(candidateFilename);
break;
case '6':
remove(candidateFilename);
remove(gradeFilename);
printf("\nRemoved!!\n");
break;
case 'S':
printf("\noption %c, the program will be ended...\n",option);
break;
default:
printf("\nWrong option!!\n");
break;
}
} while (option != 'S');
}
如果您发现有关我的代码的其他问题，请尝试解释一下这个问题。 我已经尝试过了，但还没有。
while(!feof(fp)) {
fread(&candidate,sizeof(Candidate),1,fp);
printf("\n\nId: %d \nName: %s \nDocument: %s \nGrade: %.2f",candidate->id,candidate->name,candidate->document, candidate->testGrade);
}
答案 0 :(得分：1)
Candidate *candidate = NULL;
candidate = malloc(sizeof(Candidate) + 1);
while(fread(&candidate,sizeof(Candidate),1,fp) == 1) {...}
free(candidate);
fread中的第一个参数应该是指针fread(void*,...)，而candidate已经被声明为指针，它不应该有引用运算符。正确的用法是：
while(fread(candidate,sizeof(Candidate),1,fp) == 1) {...}
请注意，&
candidate运算符
<小时/> 有时您会看到一个引用运算符，但这是一个不同的情况：
Candidate cand;
while(fread(&cand,sizeof(cand),1,fp) == 1) {...}
这是一种更简单的方法，因为cand不需要与malloc分配，也不需要free
FILE * openFile(char filename[100], char filemode[3]) {
FILE *p = fopen(filename, filemode);
if (!p) {
printf("Error to open %s file. \nThe program will be closed.",filename);
exit(1);
}
}
该函数应该返回一个文件指针。函数参数也可以简单地写为const char* filename和const char *filemode。例如：
FILE * openFile(const char* filename, const char* filemode) {
FILE *p = fopen(filename, filemode);
if (!p) printf("Error to open %s file. \nThe program will be closed.",filename);
return p;
}
我会完全摆脱这个功能，因为它基本上没用。只需使用fopen即可。完成后，请务必使用fclose关闭手柄。
grade[counter].testGrate = testGrade;
^
这是一个错字，它应该是grade[counter].testGrade。建议编译程序，警告级别设置为最大值，或者至少设置为级别4.编译器将告知错别字，错误和警告。您必须能够零错误和零警告编译程序。这是一个简单的版本：
void listAllCandidates(char* candidateFilename)
{
FILE *fin = fopen(candidateFilename, "rb");
Candidate cand;
while(fread(&cand, sizeof(cand), 1, fin))
printf("%s, %s, %d, %f\n", cand.name, cand.document, cand.id, cand.testGrade);
fclose(fin);
}
int main()
{
char candidateFilename[] = "file.bin";
FILE *fout = fopen(candidateFilename, "ab");
Candidate cand;
strcpy(cand.name, "name1");
strcpy(cand.document, "document1");
cand.id = 1;
cand.testGrade = 1.1f;
fwrite(&cand, sizeof(cand), 1, fout);
strcpy(cand.name, "name2");
strcpy(cand.document, "document2");
cand.id = 2;
cand.testGrade = 2.2f;
fwrite(&cand, sizeof(cand), 1, fout);
fclose(fout);
listAllCandidates(candidateFilename);
printf("\n");
return 0;
}