如何将指针与 getc 结合使用？

发布于 2024-09-25 14:27:57 字数 794 浏览 2 评论 0原文

我有一个函数 getNum()，它从文件中获取一个数字并返回它。当我返回 getNum() 时，我丢失了指针，它再次从文件的请求处开始。我想知道如何获取 getc 所在的位置，然后返回到那个地方。我在手册或论坛中找不到如何执行此操作。谢谢。

#include <stdio.h>
#include <stdlib.h>

int getNum();
int getLine();
int getMatrix();



main() {
int num;
int two;
num = getNum();
printf("%d\n", num);
two = getNum();
printf("%d\n", two);

}

int getNum() {
  FILE *infile;
    infile = fopen("matrix.txt","r");
  int c;
  double value = 0;

  while ((c=getc(infile)) != '\n') {
    if(c==32){
      if(value != 0){
        return(value);
      }
      //otherwise keep getting characters
    }
    else if ((c<=47)||(c>=58)){
      printf("incorrect number input %d\n", c);
      exit(1);
    }
    else {
      value = (10*value) + c - '0';
    }
  }
  return(value);
}

原文

I have a function getNum(), which gets a number from file and returns it. When I go back into getNum() I have lost the pointer and it starts at the begging of the file again. I'm wondering How do I get the location of where getc is and then go back to that place. I couldn't find how to do this in the manual or in forums. Thank you.

#include <stdio.h>
#include <stdlib.h>

int getNum();
int getLine();
int getMatrix();



main() {
int num;
int two;
num = getNum();
printf("%d\n", num);
two = getNum();
printf("%d\n", two);

}

int getNum() {
  FILE *infile;
    infile = fopen("matrix.txt","r");
  int c;
  double value = 0;

  while ((c=getc(infile)) != '\n') {
    if(c==32){
      if(value != 0){
        return(value);
      }
      //otherwise keep getting characters
    }
    else if ((c<=47)||(c>=58)){
      printf("incorrect number input %d\n", c);
      exit(1);
    }
    else {
      value = (10*value) + c - '0';
    }
  }
  return(value);
}

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静待花开 2024-10-02 14:27:57

原因是每次执行 getNum 时都会重新打开该文件。当您打开文件进行读取时，它将从文件的开头开始。相反，只需打开一次。

int main(int argc, char *argv[])
{
  ...
  FILE *infile;
  ...
  infile = fopen("matrix.txt","r");
  ...
  getNum(infile)
  ...
  fclose(infile);
  return 0;
}


int getNum(File *infile)
{
  // Same as before, just no file opening.
}

The reason is that you reopen the file each time you execute getNum. When you open a file for reading, it starts at the start of the file. Instead open it just once.

int main(int argc, char *argv[])
{
  ...
  FILE *infile;
  ...
  infile = fopen("matrix.txt","r");
  ...
  getNum(infile)
  ...
  fclose(infile);
  return 0;
}


int getNum(File *infile)
{
  // Same as before, just no file opening.
}

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ゃ人海孤独症 2024-10-02 14:27:57

每次调用 getNum 时都会重新打开该文件，因此您自然会回到开始处。

相反，在主程序中打开文件并将 FILE * 传递给 getNum()。

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妞丶爷亲个 2024-10-02 14:27:57

每次调用函数时都会重新打开文件。新打开的文件从头开始扫描。

另一种方法是在 getNum() 之外打开文件一次。您可以将 FILE* 作为参数传递给 getNum()。

另外，您没有关闭该文件。在所有调用 getNum() 后，使用 fclose() 关闭文件。

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小傻瓜 2024-10-02 14:27:57

像这样的东西：

int getNum( FILE* fp );
...

int n;
FILE* file = fopen( "file.txt" );
assert( file );
do {
    n = getNum( file );
    /* ... */
}
while ( n != -1 ); /* or something */
fclose( file );

Something like:

int getNum( FILE* fp );
...

int n;
FILE* file = fopen( "file.txt" );
assert( file );
do {
    n = getNum( file );
    /* ... */
}
while ( n != -1 ); /* or something */
fclose( file );

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