C -- 文件输入读取问题

Question

我正在从一个文件 emp 中读取，当文件(这是下面的最后一个文件 - 有效)被构造为 10 strip 有标题的记录(被跳过代码中 0 的 fseek())。但是，当它以 3x10 格式(这是下面的中间文件，未能正确读取)读入时，每个 3 block 的标题都失败了。我不确定为什么循环内的条件没有被捕获，并且循环内的第二个条件没有打印前面标有 0 的所有内容。

    int   nDeleteSwitch;
    char  sSSN[10], sName[21];
    float nSalary;
    char nextIn[3];

    printf("SSN        NAME                 SALARY\n");

    mioHashFile = fopen("emp", "r");
    fscanf (mioHashFile,"%d",&mnOverFlowRecords);
    fseek (mioHashFile, mnHeaderSize, 0); //Skip past the CRLF at end of overflow counter

    //int numHeadRec = mnOverFlowRecords/3;
    /* sequentially print all active records */
    //for(int i=0;i<(numHeadRec+mnOverFlowRecords);i++)
    for(int i=0;i<20+mnOverFlowRecords;i++)
    {
        if ((fscanf(mioHashFile,"%d",nextIn)== -1) || (fscanf(mioHashFile,"%d",nextIn)== 0) ||
            (fscanf(mioHashFile,"%d",nextIn)== 1))
        {
            fscanf(mioHashFile,"%d%s%s%f",&nDeleteSwitch,sSSN,sName,&nSalary);
            //printf("%d",nDeleteSwitch);
            if (nDeleteSwitch==0)printf("%-11s%-21s%-10.2f\n",sSSN,sName,nSalary);  // wtf why this isn't printing 
            else if (nDeleteSwitch == -1) printf("there's a -1 on row: %d",i);
        }
        else {continue;};
    }
        fclose(mioHashFile);
        printf("Print Table Complete\n");

这里我们有一个 emp 文件，它拒绝从以下位置读取 0 条目:

   0
Overflow page: 0 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
  0         x                    x      0.00
Overflow page: 1 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
  0         x                    x      0.00
Overflow page: 2 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
Overflow page: 3 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
Overflow page: 4 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
Overflow page: 5 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
Overflow page: 6 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
Overflow page: 7 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
Overflow page: 8 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
Overflow page: 9 0 -1 
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00

所以它不会读取那个，但它会读取这个:

   0
  0       123                  asd    789.00
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00
  0       345                  zxc    234.00
 -1         x                    x      0.00
 -1         x                    x      0.00
 -1         x                    x      0.00

-1 之前有一个空格，0 之前有 2 个空格。如代码所示，我试图打印任何开头带有 0 的内容，并跳过“标题”行在每个哈希 block 的前面。当我试图强制它打印(如 print < 3)时，它只是作为垃圾符号出现。

它应该做的是打印所有开头有 0 的记录并跳过标题(因为它们没有 -1,0,1 在开头)。

Answer 1

鉴于声明:

char nextIn[3];

这段代码是错误的:

if ((fscanf(mioHashFile,"%d",nextIn) == -1) || (fscanf(mioHashFile,"%d",nextIn) == 0) ||
    (fscanf(mioHashFile,"%d",nextIn) == 1))
    {

您正在传递一个包含三个字符的数组，并期望 fscanf() 将其视为 int。你的条件也很奇怪。不能保证 EOF 为 -1(尽管我不记得不是这样的系统)。在检测到 EOF 后重试没有多大意义(不是没有其他事件来清除 EOF 标记)。

When I try this fscanf(mioHashFile,"%s",nextIn); if (strcmp(nextIn, '-1') == 0) it still crashes and burns opulently due to type incompatibility. @Emmet also caught my error on the EOF (in that answer's code). How would you do it, and still maintain the scanf(), printf() formatting that I'm trying to use?

这需要一些半真实的编码。我会使用 fgets() 和 sscanf() 而不是 fscanf():

char line[4096];
int lineno = 0;
while (fgets(line, sizeof(line), mioHashFile) != 0)
{
    if (++lineno == 1)
        continue;  // Skip the offset line
    if (line[0] == 'O') // Overflow line - skip
        continue;
    if (sscanf(line, "%d %9s %20s %f", &nDeleteSwitch, sSSN, sName, &nSalary) != 4)
    {
        fprintf(stderr, "Failed to scan data from: %s", line);
        continue;
    }
    if (nDeleteSwitch == 0)
        printf("%-11s%-21s%-10.2f\n", sSSN, sName, nSalary);
    else if (nDeleteSwitch == -1)
        printf("there's a -1 on row: %d\n", lineno);
    else
        printf("The delete switch value is %d\n", nDeleteSwitch);
}

请注意，%s 会跳过前导空白，然后在下一个空白处停止扫描。