C中文件操作的分段错误

Question

#include<stdio.h>

/* this is a lexer which recognizes constants , variables ,symbols, identifiers , functions , comments and also header files . It stores the lexemes in 3 different files . One file contains all the headers and the comments . Another file will contain all the variables , another will contain all the symbols. */

int main()
{
    int i;
    char a,b[20],c;
    FILE *fp1;

    fp1=fopen("source.txt","r"); //the source file is opened in read only mode which will passed through the lexer

    //now lets remove all the white spaces and store the rest of the words in a file 

    if(fp1==NULL)
    {
        perror("failed to open source.txt");
        //return EXIT_FAILURE;
    }
    i=0;
    while(1)
    {


        a=fgetc(fp1);

        if(a !="")
        {
            b[i]=a;
        }
        else
        {


            fprintf(fp1, "%.20s\n", b);
            i=0;
            continue;
        }
        i=i+1;                  

        /*Switch(a)
        {
            case EOF :return eof;
            case '+':sym=sym+1;

            case '-':sym=sym+1;

            case '*':sym=sym+1;

            case '/':sym=sym+1;

            case '%':sym=sym+1;

            case '
        */
    }
return 0;
}

这段代码怎么会出现分段错误呢？

Answer 1

而且，字符串 b 可能不是以 null 结尾的。在代码中的某个时刻，您需要：

 b[i] = '\0';

Answer 2

看起来需要检查以确保其写入的内容没有超出数组 b 的末尾。如果它读取超过 20 个字符，则会写入超过该字符并损坏堆栈。

Answer 3

没有检查来测试文件结尾。

更改

while(1) 

为

while (!feof(fp1))

编辑：

但是段错误的原因是b末尾缺少NULL字符。您可以在将 b 写入文件之前在其末尾添加 NULL 字符：

b[i] = 0; // i must <=19
fprintf(fp1, "%.20s\n", b);

这样您还需要确保填充的内容不会超过 >19 字符到 b 中，这样您就始终有空间来写入 NULL 字符。

Answer 4

段错误？？通常无限循环...

---

使用以下...

#include<stdio.h>

/* this is a lexer which recognizes constants , variables ,symbols, identifiers , functions , comments and also header files . It stores the lexemes in 3 different files . One file contains all the headers and the comments . Another file will contain all the variables , another will contain all the symbols. */

int main()
{
    int i;
    char a,b[20],c;
    FILE *fp1;

    fp1=fopen("source.txt","r"); //the source file is opened in read only mode which will passed through the lexer

    //now lets remove all the white spaces and store the rest of the words in a file 

    if(fp1==NULL)
    {
        perror("failed to open source.txt");
        //return EXIT_FAILURE;
    }
    i=0;
    while(!feof(fp1))
    {


        a=fgetc(fp1);

        if(a !="")
        {
            b[i]=a;
        }
        else
        {

            b[i]='\0';
            fprintf(fp1, "%.20s\n", b);
            i=0;
            continue;
        }
        i=i+1;                  

        /*Switch(a)
        {
            case EOF :return eof;
            case '+':sym=sym+1;

            case '-':sym=sym+1;

            case '*':sym=sym+1;

            case '/':sym=sym+1;

            case '%':sym=sym+1;

            case '
        */
    }
return 0;
}

祝你好运！

CVS @ 2600赫兹

Answer 5

像这样使用 while ：

...
 while((a=fgetc(fp1))!=EOF)
    {
        if(a !="")
        {
            b[i]=a;
        }
...

您每次都会检查 a 是否与 EOF 不同。如果a等于EOF，则处理将停止。

我会考虑使用 fread() / fgets()，并解析结果字符串，而不是逐个字符读取。我认为这可能会提高解析器的整体性能。