Question

我有一个应该这样做的程序：

打开文件
逐个字符地读取每一行
在另一个文件中打印包含单词

我必须遵守这些条件：使用文件描述符方法打开文件，逐个字符地阅读并使用<string.h>函数。我发现了其他类似的问题，但确实有所不同...... fopen用于访问文件。

这是我的代码（在循环中由main调用的函数）：

#include<stdio.h>
#include<stdlib.h>
#include<sys/types.h>
#include<unistd.h>
#include<fcntl.h>
#include<string.h>

#define LINELENGTH 2000

int readLine(int in_fd,int out_fd,char** _line,char* word){
    /*what the functions return:
    -1 end of file,
    0 if word not founded
    >0 word founded -> return the amount of line characters
    */

    //declarations
    int counter,lineEnded,fileEnded,readReturn;
    char character;
    char* line = *_line;

    //line acquisition
    counter=lineEnded=fileEnded=readReturn=0;
    do{
        //read
        readReturn=read(in_fd,&character,1);

        //depends by the read return value:
        if(readReturn==-1){             //-error
            perror("read error");
            exit(EXIT_FAILURE);}
        else if(readReturn==0){         //-end of file
            if(counter==0) fileEnded=1;
            else lineEnded=1;}
        else if(character=='\n'){       //-character read is '\n'
            line[counter]=character;
            lineEnded=1;}
        else{                           //-character read
            line[counter]=character;
            counter++;}
    }while((counter<LINELENGTH-1) && (!lineEnded) && (!fileEnded));
    if(fileEnded) return -1;

    //if "line" were filled and then stop reading, so the input
    //line probably continue; this "if" force to add
    //a '\n' character at the end of line and increase counter
    if(!lineEnded){
       counter+=1;
       line[counter]='\n';}

    //copy the line in a new string - 3 NOT WORKING SOLUTIONS
    //1st solution: Segmentation Fault
    char* local_line;
    strncpy(local_line,line,counter+1);
    //2nd solution: so i try to use this; but this
    //delete the last character to insert '\n'
    char* local_line;
    local_line = strtok(line,"\n");
    local_line[counter-1]='\n';
    //3rd solution: seems to work but...
    char* local_line = (char*)malloc(sizeof(char)*(counter+1));
    local_line = strtok(line,"\n");
    local_line[counter+1] = '\n'; //but this line seems to be ignored;
           //line written in output file do not contain \n at the end

    //search "word" in "local_line"
    char* strstrReturn = strstr(local_line,word);

    //write line on file represented by out_fd (if word founded)
    if(strstrReturn==NULL){
        free(local_line); //only with the 3rd solution.. but this line
                          //causes Memory Corruption after some fuction cycles!
        return 0;}
    else{
        write(out_fd,local_line,counter);
        free(local_line); //only with the 3rd solution.. but causes
                          //Segmentation Fault!
        return counter;
    }
}


main(int argc,char* argv[]){

    //check arguments
    if(argc!=3){
        printf("syntax: exec fileName wordSearch\n");
        exit(EXIT_FAILURE);}

    //declarations
    int fd_1,fd_2;
    int readLineReturn=0;
    //int debug;
    char* line = (char*)malloc(sizeof(char)*LINELENGTH);

    //open file for reading
    fd_1 = open(argv[1],O_RDONLY);
    if(fd_1<0){
        perror("error opening fd_1");
        exit(EXIT_FAILURE);}

    //open file for writing
    fd_2 = open("outFile.txt",O_WRONLY|O_TRUNC|O_CREAT,0664);
    if(fd_2<0){
        perror("error opening fd_2");
        exit(EXIT_FAILURE);}

    //line acquisition
    int readLineReturn;
    do{
        readLineReturn = readLine(fd_1,fd_2,&line,argv[2]);
    }while(readLineReturn!=-1);

    close(fd_2);
    close(fd_1);
    free(line);
    printf("\n");
    exit(EXIT_SUCCESS);
}

这是代码中存在相关执行错误问题的部分（您可以在函数中找到它）。

//copy the line in a new string - 3 NOT WORKING solutions
    //1st solution: Segmentation Fault
    char* local_line;
    strncpy(local_line,line,counter+1);
    //2nd solution: so i try to use this; but this
    //delete the last character to insert '\n'
    char* local_line;
    local_line = strtok(line,"\n");
    local_line[counter-1]='\n';
    //3rd solution:
    char* local_line = (char*)malloc(sizeof(char)*(counter+1));
    local_line = strtok(line,"\n");
    local_line[counter+1] = '\n';

我认为存在结构性或概念性错误，但我无法找到它。

Answer 1

 char* local_line;
 strncpy(local_line,line,counter+1);

在使用strncpy之前，您需要使用local_line或类似功能将内存分配给malloc。

从文件中读取行，并返回包含单词的行

1 个答案: