我需要逐行读取文件，并使用从每行收集的信息来进行一些操作。到目前为止，我的代码只能逐行读取文件并在控制台中打印。
#include <stdio.h>
#include <stdlib.h>
#include "structure.h"
int main()
{
printf("Hello world!n");
int x = 43; // number of lines in my text file
FILE *fptr;
struct values *valuesPtr = malloc(sizeof(struct values) * x);
if (!valuesPtr)
return -1;
if((fptr = fopen("energy.txt", "r")) == NULL) {
printf ("Error opening file ");
return 0;
}
while (fptr != NULL) {
for(int i = 0; i < x; i++ ) {
fscanf(fptr, "%s %s %d", valuesPtr[i].start_vertex, valuesPtr[i].destination_vertex, &valuesPtr[i].num);
printf("nStart vertex: %s nDestination vertex: %s nWeight: %dnn", valuesPtr[i].start_vertex, valuesPtr[i].destination_vertex, valuesPtr[i].num);
}
free(valuesPtr);
}
fclose(fptr);
return 0;
}
我的structure.h文件有以下代码：
struct values{
int num;
char start_vertex[250];
char destination_vertex[250];
} x;
energy.txt文件包含以下内容：
York Hull 60
Leeds Doncaster -47
Liverpool Nottingham 161
Manchester Sheffield 61
Reading Oxford -43
Oxford Birmingham 103
Birmingham Leicester 63
Liverpool Blackpool 79
Carlisle Newcastle 92
Nottingham Birmingham 77
Leeds York 39
Glasgow Edinburgh 74
Moffat Carlisle 65
Doncaster Hull 76
Northampton Birmingham 90
Leicester Lincoln 82
Sheffield Birmingham 122
Lincoln Doncaster 63
Sheffield Doncaster 29
Bristol Reading 130
Hull Nottingham 145
Blackpool Leeds 116
Birmingham Bristol 139
Manchester Leeds 64
Carlisle Blackpool 140
Leicester Northampton -61
Newcastle York 135
Glasgow Moffat -28
Leicester Sheffield 100
Carlisle Liverpool -30
Birmingham Manchester 129
Oxford Bristol 116
Leeds Hull 89
Edinburgh Carlisle 154
Nottingham Sheffield 61
Liverpool Manchester 56
Carlisle Glasgow 50
Sheffield Lincoln 74
York Doncaster 55
Newcastle Edinburgh 177
Leeds Sheffield 53
Northampton Oxford 68
Manchester Carlisle 20
我被告知使用getline()函数和sscanf()来存储文件中的数据。但我不确定该怎么做。
您的代码中存在几个问题
具有
if((fptr = fopen("energy.txt", "r")) == NULL)
{
printf ("Error opening file ");
return 0;
}
while (fptr != NULL)
如果fptr为NULL，则不能在while时到达，并且fptrwhile的正文中的值永远不会更改，因此一个是无限循环
另一个问题是，在的之后，您可以释放值ptr，因此从第二轮开始，您将在释放的内存中进行写入，并使用意外内存。很可能而是无用的，可以删除(当然不是的(。
假设在完成时，您尝试释放fptr，但这不是关闭描述的方法，您必须调用fclose(fptr(而不是free。您的free有一个未定义的行为
我鼓励您检查fscanf返回的值，目前您无法知道它是否成功。请注意，fscanf也可以写出包含字符串的字段，因为您不限制要读取的字符数。
当您无法打开文件时，您可以使用错误给出原因：
perror("Error opening file");
编辑后的提案：
#include <stdio.h>
#include <stdlib.h>
typedef struct value {
int num;
char start_vertex[250];
char destination_vertex[250];
} value;
int main()
{
const int nLines = 43; // number of lines in my text file
FILE * fptr;
value * valuesPtr = malloc(sizeof(value) * nLines);
if (!valuesPtr) {
puts("cannot allocate memory");
return -1;
}
if((fptr = fopen("energy.txt", "r")) == NULL)
{
perror("Error opening file");
return -1;
}
for(int i = 0; i < nLines; i++ )
{
if (fscanf(fptr, "%249s %249s %d",
valuesPtr[i].start_vertex,
valuesPtr[i].destination_vertex,
&valuesPtr[i].num) != 3) {
printf("errored file line %dn", i);
break;
}
printf("nStart vertex: %s nDestination vertex: %s nWeight: %dnn",
valuesPtr[i].start_vertex, valuesPtr[i].destination_vertex, valuesPtr[i].num);
}
free(valuesPtr);
fclose(fptr);
return 0;
}
编译和执行：
pi@raspberrypi:/tmp $ gcc -Wall l.c
pi@raspberrypi:/tmp $ ./a.out
Start vertex: York
Destination vertex: Hull
Weight: 60
Start vertex: Leeds
Destination vertex: Doncaster
Weight: -47
Start vertex: Liverpool
Destination vertex: Nottingham
Weight: 161
Start vertex: Manchester
Destination vertex: Sheffield
Weight: 61
Start vertex: Reading
Destination vertex: Oxford
Weight: -43
Start vertex: Oxford
Destination vertex: Birmingham
Weight: 103
Start vertex: Birmingham
Destination vertex: Leicester
Weight: 63
Start vertex: Liverpool
Destination vertex: Blackpool
Weight: 79
Start vertex: Carlisle
Destination vertex: Newcastle
Weight: 92
Start vertex: Nottingham
Destination vertex: Birmingham
Weight: 77
Start vertex: Leeds
Destination vertex: York
Weight: 39
Start vertex: Glasgow
Destination vertex: Edinburgh
Weight: 74
Start vertex: Moffat
Destination vertex: Carlisle
Weight: 65
Start vertex: Doncaster
Destination vertex: Hull
Weight: 76
Start vertex: Northampton
Destination vertex: Birmingham
Weight: 90
Start vertex: Leicester
Destination vertex: Lincoln
Weight: 82
Start vertex: Sheffield
Destination vertex: Birmingham
Weight: 122
Start vertex: Lincoln
Destination vertex: Doncaster
Weight: 63
Start vertex: Sheffield
Destination vertex: Doncaster
Weight: 29
Start vertex: Bristol
Destination vertex: Reading
Weight: 130
Start vertex: Hull
Destination vertex: Nottingham
Weight: 145
Start vertex: Blackpool
Destination vertex: Leeds
Weight: 116
Start vertex: Birmingham
Destination vertex: Bristol
Weight: 139
Start vertex: Manchester
Destination vertex: Leeds
Weight: 64
Start vertex: Carlisle
Destination vertex: Blackpool
Weight: 140
Start vertex: Leicester
Destination vertex: Northampton
Weight: -61
Start vertex: Newcastle
Destination vertex: York
Weight: 135
Start vertex: Glasgow
Destination vertex: Moffat
Weight: -28
Start vertex: Leicester
Destination vertex: Sheffield
Weight: 100
Start vertex: Carlisle
Destination vertex: Liverpool
Weight: -30
Start vertex: Birmingham
Destination vertex: Manchester
Weight: 129
Start vertex: Oxford
Destination vertex: Bristol
Weight: 116
Start vertex: Leeds
Destination vertex: Hull
Weight: 89
Start vertex: Edinburgh
Destination vertex: Carlisle
Weight: 154
Start vertex: Nottingham
Destination vertex: Sheffield
Weight: 61
Start vertex: Liverpool
Destination vertex: Manchester
Weight: 56
Start vertex: Carlisle
Destination vertex: Glasgow
Weight: 50
Start vertex: Sheffield
Destination vertex: Lincoln
Weight: 74
Start vertex: York
Destination vertex: Doncaster
Weight: 55
Start vertex: Newcastle
Destination vertex: Edinburgh
Weight: 177
Start vertex: Leeds
Destination vertex: Sheffield
Weight: 53
Start vertex: Northampton
Destination vertex: Oxford
Weight: 68
Start vertex: Manchester
Destination vertex: Carlisle
Weight: 20
pi@raspberrypi:/tmp $
我冒昧地将values重命名为value，因为结构保存了一个元素而不是几个元素，无论如何，我鼓励您将其重命名为更精确的元素，value非常通用。我还使用了typedef，不必在每个使用它的地方都需要结构。
看看细节，例如，对于字符串，我使用格式%249s，因为数组有250个字符(我删除了最后一个空字符的1个(，当然我检查它是否读取了3个元素。