讀取線，並返回行包含字

Question

我有一個程序，應該這樣做：

1. 打開文件
2. 讀取字符每行的字符
3. 打印在另一個文件含有字

線I必須尊重此條件：與文件描述符方法打開的文件，由字符讀取的字符，並使用<string.h>功能。 我發現了其他類似的問題，但真的不同..和fopen用於訪問文件。

這是我的代碼（由主在一個週期內調用的函數）：

#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); 
} 

這是代碼與相關執行錯誤問題的部分（你可以找到它的功能）。

//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'; 

我覺得有一個結構性或概念性的錯誤，但我找不到它。

Answer 1

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

在此使用strncpy之前，你需要分配內存以local_line使用malloc或類似的功能。