[英]C fscanf returning null
我的作業有一個問題,其中一部分需要掃描和讀取一些特定的輸入。 相關的C代碼是:
typedef struct Train {
int train_number;
int priority; // 0 is low priority, 1 is high priority
int direction; // 0 is Westbound, 1 is Eastbound
float loading_time;
float crossing_time;
int loaded;
} Train;
#define MAX_TRAIN_COUNT 777
Train station[MAX_TRAIN_COUNT];
int main(int argc, char* argv[]) {
//read the input file
FILE *input;
char c;
int train_count = 0;
input = fopen(argv[1], "r");
while((c = getc(input)) != EOF) {
if(c == '\n')
train_count++;
}
int i;
for (i = 0; i < train_count; i++) {
char dir;
int load, cross;
fscanf(input, "%c %d %d\n", &dir, &load, &cross);
printf("%c %d %d\n", dir, load, cross);
}
fclose(input);
輸入是3行,由1個char和兩個用空格分隔的整數組成。
e 10 6
W 6 7
E 3 10
我得到的輸出是:
4195728 0
4195728之前的位置。我似乎找不到解決此問題的解決方案。
似乎是什么問題?
代碼在第二次讀取數據之前無法倒帶文件。 缺乏檢查輸入功能是否成功的原因是無法暴露問題。 @WhozCraig 。
int i;
rewind(input); // add
for (i = 0; i < train_count; i++) {
// fscanf(input, "%c %d %d\n", &dir, &load, &cross);
if (fscanf(input, "%c %d %d\n", &dir, &load, &cross) != 3) Handle_Error();
更好的方法是在輔助函數中處理讀取數據文件的行。
與fscanf()
相比,使用fgets()
處理麻煩的輸入要好得多。 @放松
int ReadTrainData(Train *data, FILE *stream) {
char buffer[200];
if (fgets(buffer, sizeof buffer, stream) == NULL) {
return EOF;
}
// Various ways to parse data.
// This one look for a completed scan and checks that `n` was changed.
int n = 0;
// v-- add space to consume optional leading white-space (if desired)
sscanf(buffer, " %c %d %d %n", &data.direction, &data.loading_time,
&data.crossing_time, &n);
if (n == 0) return 0; // data incomplete
if (buffer[n]) return 0; // extra junk in line
// maybe valid data
if (strchr("NSEWnsew", &data.direction) == NULL) return 0;
if (data.loading_time < 0 || data.loading_time > TRAIN_TIME_MAX) return 0;
// add other validation tests as needed
return 1;
}
樣品用法
size_t train_count = 0;
if (input) {
Train data = {0};
while(ReadTrainData(&data, input) == 1) {
train_count++;
printf("%c %d %d\n", data.direction, data.loading_time, data.crossing_time);
}
fclose(input);
}
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