尝试使用行和列进行文件I / O，以及放置FILE的问题*

分类：编程问答

如何解决尝试使用行和列进行文件I / O，以及放置FILE的问题*

我正在尝试编写2个函数：

  • 将FILE *移动到传递的索引中的一个
  • 另一个将FILE *中的内容从2个索引之间复制到字符串中的

发生了非常莫名其妙的错误，我已经尝试修复了好几个小时，并且即将崩溃，请指出我的愚蠢。

观察到的行为：

  1. chknbuff()跳过了最后一个字符，因此我用磁带录制了一些可以解决该问题的代码。
  2. 读取超过第一行（例如，ln = 2，col = x）会触发其他文件中chkncpy()中的EOF错误。
  3. 抑制chknmove()的EOF警告将给出Segmentation Fault s，这意味着确实遇到了EOF。

代码：

#include <stdio.h>
/*-------Function-Definitions------------*/
int chknmove(FILE *tomove,long long line,long long col){
// moves FILE * to line & col passed
    rewind(tomove); int chk,f; long long i,q; i=0; q=0; f=0;
    if(line>=1 && col>=1){
        while(i < line){
            chk = fgetc(tomove);
            if(chk == EOF){
                printf("\n Invalid Index.\n");f=-1;break;
            }
            else if(chk == '\n'){
                if(i == line - 1){
                    printf("\n Invalid Index.\n");f=-1;break;
                }
                i++; q = 0;
            }
            else if(i == line - 1 && q == col - 1){
                break;
            }
            else
                q++;
        }
        if(f==0)
            fseek(tomove,-1,SEEK_CUR);
    }
    else{
        printf("\n Invalid Index.\n");f=-1;
    }
    return f;
}
int chknbuff(FILE *source,char *dest,long long beginln,long long begincol,long long endln,long long endcol){
// copies file contents from beginning line&cols to end lines&cols to a string.
    int z = chknmove(source,beginln,begincol);
    if(z==0){
        int chk; long long i,q,m; i=0; q=0; m=0; //endcol++;
        if(endln>=1 && endcol>=1 && endln>=beginln){
            while(i < endln){
                chk = fgetc(source);
                if(chk == EOF){
                    printf("\n Invalid Index1.\n");z=-1;break;
                }
                else if(chk == '\n'){
                    if(i == endln-1){
                        printf("\n Invalid Index2.\n");z=-1;break;
                    }
                    dest[m]=chk;m++; i++; q = 0;
                }
                else if(i == endln-1 && q == endcol-1 ){
                    break;
                }
                else{
                    dest[m]=chk;m++; q++;
                }
            }
            if(z==0){
                fseek(source,SEEK_CUR);
                chk = fgetc(source);
                if(chk!=EOF)
                    dest[m]=chk; m++;
            }
            dest[m++]='\0';
        }
        else{
            printf("\n Invalid Index3.\n");z=-1;
        }
    }
    return z;
}
/*---------------------------------------------*/

int main(){
    FILE * write = fopen("xyz","w");
    if(write == NULL)
        perror("\n Error ");
    else{
        printf("\n Filename : "); char fpart[501]; scarf("%500[^\n]",fpart); FILE * part = fopen(fpart,"r");
        if(part==NULL)
            perror("\n Error ");
        else{
            long long beginln,begincol,endln,endcol; char sep1,sep2;
            printf("\n Starting Index : ");     scanf("%lld%c%lld",&beginln,&sep1,&begincol); eat();
            printf("\n Terminating Index : "); scanf("%lld%c%lld",&endln,&sep2,&endcol); eat();
            char buff[MAX_F_BUFF];int f = chknbuff(part,buff,endcol);
            if(f==0)
                fputs(buff,write);  
        }
        int d = fclose(write);
        if(d==EOF)
            perror("\n Failed ");
        else
            printf("\n Success.\n"); 
    }
    return 0;
}

如果需要任何其他信息，请发表评论，我会尝试添加它

解决方法

在此自我解答中，我发布了为我解决此问题的方法。我在这个问题上的功能有些拙劣和混乱，在这里不再是。

我已经解决了它从dxiv的答案here借来的问题，并解决了如何处理'\n'字符的问题。 afaik 效果很好。

希望对将来的其他人有帮助。

我需要的功能：


int chknmove(FILE *tomove,long long line,long long col){
    /* Moves FILE* to given ((line,col) -1 char),such that next char read from FILE* will be @ (line,col)
     Checks validity of index as it moves : if col not in line || EOF encountered,returns -1. */

    rewind(tomove); // rewind file 'just in case'

    int f = 0 ; // control variable which stores state (succeeded/failed) of chknmove()

    if (line < 1 || col < 1) 
    {
        f=-1; 
        printf("\n Illegal Index.\n");
        // Follows 1-based line/col index : -ve values are illegal
        return -1;
    }
    else {
        long long i,q; i = q = 0; // i = lines encountered ; q = chars encountered in line i ; both are 0-based

        while(i < line){
            int chk = fgetc(tomove); // 
            if(chk == EOF){
                printf("\nInvalid %s - beyond EOF.\n",(i == line -1 ) ? "Column" : "Line"); 
                f = -1; break;
            }
            else if(chk == '\n'){
                if(i==line-1 && q == col-1) 
                /*  1. This allows for user to directly point to the '\n' char,allowing him to append to line 
                    2.(line/col - 1) : since i & q are 0-based   */
                    break;
                else{
                    if(i == line-1 ){
                        // except if target index was the '\n',reading beyond newline @ target line is invalid,since '\n' terminates line
                        printf("\nInvalid column for line %lld.\n",line); 
                        f=-1; break;
                    }
                    i++; q=0; // if not @ target line,reset and continue 
                }
            }
            else if(i == line-1  && q == col-1 ) // if dest index reached,break .
                break;
            else // if non-EOF,non-\n char encountered,increment q and continue.
                q++;
        }

        if(f==0){
            fseek(tomove,-1,SEEK_CUR); // So that the after returning/exiting chknmove(),the char read from FILE* is @ line,col
            return 0;
        }
        else
            return -1;
    }
}

AND 

int chknbuff(FILE* source,char *dest,long long beginln,long long begincol,long long endln,long long endcol) {
    /* Copies everything from FILE *source to char *dest within begining index and terminating index,if they're valid
        Returns -1 if they're invalid.*/

    if (beginln < 1 || begincol < 1 || endln < beginln || endcol < ((endln == beginln) ? begincol : 1))
        // -ve indexes and reading/writing backwards is illegal
        return -1;

    long long i,q; // i -> lines && q -> chars 
    int f=0; long long m = 0;
    if(chknmove(source,beginln,begincol)==0){ 
        // checked if begining index is valid and if so,moved to it.

        i=beginln; q=begincol; // i & q have same base as line & col,so 1-based

        while(1){
            int ch = fgetc(source);
            if(ch==EOF){
                printf("\nInvalid Terminating Index.\n");
                f=-1; break;
            }
            else if(ch=='\n'){
                if(i==endln && q==endcol){
                    dest[m]=ch; m++;
                    break;
                }
                else{
                    if(i==endln){
                        printf("Invalid column for line %lld.\n",endln);
                        f=-1; break;
                    }
                    i++; q=1; // q set to 1 -> q is 1-based !
                    dest[m]=ch; m++;
                }
            }
            else if(i==endln && q==endcol){
                dest[m]=ch; m++; break;
            }

            else{
                q++; dest[m]=ch; m++;
            }
        }
    }
    else
        f=-1;

    dest[m]='\0'; // null terminate the buffer 
    if(f==0)    return 0;
    else    return -1;
}

如果有任何遗漏的错误/细节，请发表评论，我会尽快答复

,

以下内容扩展了我的评论“ 您可以使用一个函数完成所有操作”，并且只需通过文件一次即可完成操作。范围内的字符用putchar(chk);打印，可以用fputc(chk,write);或dest[count] = chk;替换以保存到文件或字符串缓冲区。

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

// return number of characters in 'copy' range between (beginline,begincol) and (endline,endcol)
// line/col are 1-based and the 'copy' range is inclusive of both begin/end positions
long long copy_range(FILE* fyl,long long endcol) {
    long long line,col,count; int chk;

    if (beginln < 1 || begincol < 1 || endln < beginln || (endln == beginln && endcol < begincol))
        return -1;

    // assume current file position is at the beginning,maybe 'rewind' if that's not guaranteed
    line = 1; col = 1; count = -1;

    // read the file sequentially
    // start saving characters once (beginline,begincol) is reached
    // break out of the loop after (endline,endcol) is reached
    do {
        // attempt to read character at position (line,col)
        chk = fgetc(fyl);

        // attempt failed,return error
        // check count to see whether it happened before or within the 'copy' range
        // check line to see if the entire line is past EOF vs. just the target column
        if (chk == EOF) {
            printf("\nInvalid %s %s.\n",(count < 0) ? "Beginning" : "Ending",(line == beginln) ? "Column" : "Line");
            break;
        }

        // found newline character
        if (chk == '\n') {
            // error if looking for (beginln,begincol) and newline found on beginln before begincol
            //    or if looking for (endln,endcol) and newline found on endln before endcol
            if (line == ((count < 0) ? beginln : endln)) {
                printf("\nInvalid %s Column.\n",(count < 0) ? "Beginning" : "Ending");
                break;
            }

            // comment the following if *not* preserving newlines in 'copy' range
            if (count >= 0) {
                putchar(chk); count++;
            }

            // update position and move on
            line++; col = 1; continue;
        }

        if (line == beginln && col == begincol) {
            // enter the 'copy' range,start counting
            printf("--- begin ---\n"); count = 0;
        }
        if (count >= 0) {
            // save character if within the 'copy' range
            putchar(chk); count++;
        }
        if (line == endln && col == endcol) {
            // leave the 'copy' range,return the count
            // if saving to a string,add the nul-terminator here,but do not increment counter
            printf("\n---- end ----\n"); break;
        }
        col++;
    } while (line <= endln);

    return count;
}

int main() {
    char fpart[501];
    printf("\nEnter Filename:\n");
    if (scanf("%500[^\n]",fpart) != 1) return -1;;

    FILE* part = fopen(fpart,"r");
    if (part == NULL) return errno;

    long long beginln,begincol,endln,endcol;
    printf("\nEnter Starting Index:\n");
    if (scanf("%lld %lld",&beginln,&begincol) != 2) return -2;;
    printf("\nEnter Terminating Index:\n");
    if (scanf("%lld %lld",&endln,&endcol) != 2) return -3;

    return copy_range(part,endcol) > 0;
}

[ EDIT ]”在注释之后，澄清为意味着将换行符计数为之前的最后一行，这是对上述内容的修改，将'\n'检查移到了字符之后被处理，并删除现在多余的换行符。

long long copy_range(FILE* fyl,count; int chk;

    if (beginln < 1 || begincol < 1 || endln < beginln || endcol < ((endln == beginln) ? begincol : 1))
        return -1;

    line = 1; col = 1; count = -1;

    do {
        chk = fgetc(fyl);

        if (chk == EOF) {
            printf("\nInvalid %s %s.\n",(line == beginln) ? "Column" : "Line");
            break;
        }

        if (line == beginln && col == begincol) {
            printf("--- begin ---\n"); count = 0;
        }
        if (count >= 0) {
            putchar(chk); count++;
        }
        if (line == endln && col == endcol) {
            printf("\n---- end ----\n"); break;
        }

        if (chk == '\n') {
            if (line == ((count < 0) ? beginln : endln)) {
                printf("\nInvalid %s Column.\n",(count < 0) ? "Beginning" : "Ending");
                break;
            }
            line++; col = 1;
        }
        else
            col++;
    } while (line <= endln);

    return count;
}

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