从c中的文件中读取值

Question

我有两个文件要读取。其中之一包含两列，例如：

Account Number      Amount
100                 27.14
300                 62.11
400                 100.56
900                 82.17

另一个文件有5列，内容如下：

Account Number      Name           Surname        Balance        
100                 Alan           Jones          348.17
300                 Mary           Smith          27.19
500                 Sam            Sharp          0.00
700                 Suzy           Green          -14.22

我想比较两个文件的账号，把第一个文件的余额加上第二个文件的余额。到目前为止，我尝试从第一个文件中获取帐号并将其打印在屏幕上。我尝试使用fread 函数，但它不起作用。

我的尝试是：

struct clientData{
    unsigned int acctNum;
    char name[20];
    char surname[20];
    double balance;
};
int main(){

FILE *fPtr, *fPtr2;
    
    if(!(fPtr = fopen("transaction_file.txt", "r"))){
        printf("[ERROR] File could not be found!\n");
        return;
    }
    fseek(fPtr, (0) * sizeof(struct clientData), SEEK_SET);
    
    struct clientData client = {0, "", "", 0.0};
    
    //read record from file
    fread(&client, sizeof(struct clientData), 1, fPtr);
    printf("%-6u%10.2lf\n\n", client.acctNum, client.balance);
}

Answer 1

类似于@William Pursell，但具有更强的解析测试。

// if (2 == sscanf(line, "%d %f", &n.number, &n.balance) ||
//     4 == sscanf(line, "%d %31s %31s %f", &n.number, n.name, n.surname, &n.balance)

int end = 0;
sscanf(line, "%d %f %n", &n.number, &n.balance, &end);
if (end > 0 && line[end] == 0) {
  ; // Handle file 1 type line
} else {
  end = 0;
  sscanf(line, "%d %31s %31s %f %n", &n.number, n.name, n.surname, &n.balance, &end);
  if (end > 0 && line[end] == 0) {
    ; // Handle file 2 type line
  }
}

Answer 2

您需要解析输入。尽管它完全不适合生产工作（即使不是不可能，也很难稳健地避免意外输入上的未定义行为），但使用scanf 是一种简单的方法。 您将希望使用一种使查找变得容易的数据结构。最简单的（IMO）实现是不平衡树。比如：

#include <ctype.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void * xmalloc(size_t s);
FILE * xfopen(const char *path, const char *mode);
int die(const char *fmt, ... );

struct account {
    int number;
    float balance;
    char name[32];
    char surname[32];
    struct account *next[2];
};

void
insert(struct account **root, const struct account *n)
{
    struct account *r = *root;

    if( r == NULL ){
        r = *root = xmalloc(sizeof **root);
        memcpy(r, n, sizeof *n);
    } else if( n->number == r->number ){
        r->balance += n->balance;
        if( *r->name == '\0' ){
            strcpy(r->name, n->name);
            strcpy(r->surname, n->surname);
        }
    } else {
        insert(r->next + (n->number > r->number), n);
    }
}

const char *hdr[2] = {
    "Account Number      Amount\n",
    "Account Number      Name           Surname        Balance\n"
};
void
read_file(struct account **root, FILE *ifp)
{
    size_t cap = 0;
    char *line = NULL;
    struct account n = {0};
    while( getline(&line, &cap, ifp) > 1 ){
        if( 2 == sscanf(line, "%d %f", &n.number, &n.balance) \
        || 4 == sscanf(line, "%d %31s %31s %f",
            &n.number, n.name, n.surname, &n.balance)
        ) {
            insert(root, &n);
        } else if( strcmp(line, hdr[0]) && strcmp(line, hdr[1]) ) {
            die("invalid input: %s\n", line);
        }
    }
    free(line);
}

void
print(struct account *r)
{
    if( r ){
        print(r->next[0]);
        printf("%d %-31s %-31s %.2f\n",
            r->number, r->name, r->surname, r->balance
        );
        print(r->next[1]);
    }
}

int
main(int argc, char **argv)
{
    struct account *root = NULL;
    if( argc > 1 ){
        FILE *fp;
        for(char *const* path = argv + 1; *path; path += 1 ){
            read_file(&root, fp = xfopen(*path, "r"));
            if( fclose(fp) ){
                perror(*path);
            }
        }
    } else {
        read_file(&root, stdin);
    }
    print(root);
}

FILE *
xfopen(const char *path, const char *mode)
{
    FILE *fp = path[0] != '-' || path[1] != '\0' ? fopen(path, mode) :
        *mode == 'r' ? stdin : stdout;
    if( fp == NULL ){
        perror(path);
        exit(EXIT_FAILURE);
    }
    return fp;
}

void *
xmalloc(size_t s)
{
    void *rv = malloc(s);
    if( rv == NULL ){
        perror("malloc");
        exit(EXIT_FAILURE);
    }
    return rv;
}

int
die(const char *fmt, ... )
{
    va_list ap;
    va_start(ap, fmt);
    vfprintf(stderr, fmt, ap);
    va_end(ap);
    exit(EXIT_FAILURE);
}