问题描述
提供了代码M.R.E。
症状是“ 简单”：
- 尝试运行
hello\nhello\nhelloEOF并在程序中插入'_'@ln=2和col=1（或更确切地说是任何line>1 && col==1），奇怪地 ，但吃光了'\n'，导致第2行与第1行-hello_hello\nhelloEOF而不是hello\n_hello\nhelloEOF融合了 。 - 尝试在文件
hello\nhello\nhelloEOF的最后一行输入一个字符，并在'_和ln=3中插入'col=5'（或者在任何字符{{1}处插入） }（以EOF结尾的行）会跳过该行的最后一个 actual 字符：col>1而不是hello\nhello\nhell_EOF。 - 尝试在最后一行（EOF终止的行中的
hello\nhello\nhell_oEOF）中使用第一个字符会导致抛出错误消息（col==1）。
就我的直觉而言，我认为处理线路终止（\n Invalid Index.，'\n'）及其计数方法以及循环计数器时存在缺陷，但是我我不明白。
想法/算法：
- 从用户获取源文件
- 从用户（行，列）获取索引
- 从源复制到tmp文件，直到（用户索引-1 col）。
- 现在，允许用户将字符串写入tmp文件的缓冲区。
- 用户终止输入后，将其索引复制到tmp直到
EOF。 - 重命名/删除+重命名tmp作为用户的源文件名。
下面的代码可以真正说明一切：
EOF如果有任何遗漏的细节或错误的错误，请发表评论，我会予以纠正。
解决方法
您的代码太复杂了：
-
复制文件开头的不同情况应合并到一个函数调用中，该函数可以复制数据，直到行
col上列line的字节为止（不包括该字节）。 >
-
然后从用户输入中复制。
-
最后，复制其余的输入文件。
-
该代码假定行和列的编号从
1开始。这可能很明显，但是您应该指定它，因为它可能对每个人都不明显。 -
该样式很难理解：您应该在关键字
,和;之后以及{之前在二进制运算符周围使用水平空间。在一行上填充多个语句也不是一个好主意。
这里是简化版。通常，大多数代码用于错误处理：
#include <stdio.h>
#include <string.h>
void flush_line(FILE *fp) { /* read the rest of the current line */
int c;
while ((c = getc(fp)) != '\n' && c != EOF)
continue;
}
int copy_file(FILE *from,FILE *to) {
int c;
while ((c = getc(from)) != EOF) {
if (putc(c,to) == EOF)
return EOF;
}
return 0;
}
int copy_lines(FILE *from,int line1,int col1,FILE *to) {
int c,line = 1,col = 1;
for (;;) {
if (line >= line1 || (line == line1 && col >= col1))
break;
if ((c = getc(from)) == EOF)
break;
if (putc(c,to) == EOF)
return EOF;
col++;
if (c == '\n') {
line++;
col = 1;
}
}
return 0;
}
int writer(FILE *write) {
char in[501]; /* str that stores input line-by-line */
char *p;
printf("\n Terminate Input with \"/end/\".\n\n Type below :\n\n");
while (fgets(in,501,stdin)) {
if ((p = strstr(in,"/end/")) != NULL) {
/* if line has "/end/",all chars till /end/ are written to file and input loop breaks */
int o = p - in;
if (fprintf(write,"%.*s",o,in) < 0)
return EOF;
break;
} else {
/* writes line to file */
if (fputs(in,write) < 0)
return EOF;
}
}
return 0;
}
int main() {
/* main to add/insert to file @ given index */
const char *temp_filename = "Temp.Ctt";
char fadd[501];/* filename str */
printf("\n Filename : ");
if (scanf("%500[^\n]",fadd) != 1)
return 1;
flush_line(stdin);
FILE *add = fopen(fadd,"r");
if (add == NULL) {
perror("\n Cannot open input file");
return 1;
}
int line,col;
/* read the index: 1 based line and column numbers */
printf("\n Index : ");
if (scanf("%d%*c%d",&line,&col) != 2) {
fprintf(stderr,"invalid input\n");
return 1;
}
flush_line(stdin);
FILE *tmp = fopen(temp_filename,"w");
if (tmp == NULL) {
perror("\n Cannot create temporary file");
fclose(add);
return 1;
}
if (copy_lines(add,line,col,tmp)) {
perror("\n Error copying beginning of file");
fclose(add);
fclose(tmp);
remove(temp_filename);
return 1;
}
if (writer(tmp)) {
perror("\n Error writing user input");
fclose(add);
fclose(tmp);
remove(temp_filename);
return 1;
}
if (copy_file(add,tmp)) {
perror("\n Error copying remaining file contents");
fclose(add);
fclose(tmp);
remove(temp_filename);
return 1;
}
fclose(add);
if (fclose(tmp) < 0) {
/* if closing tmp was unsuccessful,the file on disk may be corrupted/incomplete,so must be removed */
perror("\n Error closing temporary file");
remove(temp_filename);
return 1;
}
if (rename(temp_filename,fadd) == 0) {
printf("\n Success.\n");
return 0;
}
/* on Windows & some other non-POSIX systems,file cannot be renamed to pre-existing filename,hence delete original */
if (remove(fadd)) {
perror("\n Cannot remove input file");
remove(temp_filename);
return 1;
}
if (rename(temp_filename,fadd) == 0) {
printf("\n Success.\n");
return 1;
}
/* if rename still unsuccessful,try and copy contents */
tmp = fopen(temp_filename,"r");
if (tmp == NULL) {
perror("\n Cannot re-open temporary file,output is in Temp.Ctt");
return 1;
}
add = fopen(fadd,"w");
if (add == NULL) {
perror("\n Cannot re-open input file,output is in Temp.Ctt");
fclose(tmp);
return 1;
}
if (copy_file(tmp,add)) {
perror("\n Error copying temporary file to input file");
fclose(add);
fclose(tmp);
return 1;
}
fclose(tmp);
if (fclose(add) < 0) {
perror("\n Error closing input file");
return 1;
}
/* throw an error,remove tmp file and give up */
remove(temp_filename);
printf("\n Success.\n");
return 0;
}
这是我的自我解答，chknmove()和chkncpy()的问题导致了“ glitching ”，以下已解决。
下面的代码可以立即编译，并经过大量注释和隔开，因此实际上比封装在chknmove()和chkncpy()中的主要思想大。 -因此这些已放置在代码的顶部。
希望这个问题/答案将来对其他人有用。
#include <stdio.h> // For file & console I/O
#include <string.h> // For strstr() in writer()
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;
}
}
int chkncpy(FILE* source,FILE *dest,long long beginln,long long begincol,long long endln,long long endcol) {
/* Copies everything from FILE *source to FILE *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;
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){
fputc(ch,dest);
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 !
fputc(ch,dest);
}
}
else if(i==endln && q==endcol){
fputc(ch,dest); break;
}
else{
q++; fputc(ch,dest);
}
}
}
else
f=-1;
if(f==0) return 0;
else return -1;
}
long long lcc(FILE *fyl,long long line){
// L.C.C. == line char count,i.e,count of chars in a line (including the \n).
int f = chknmove(fyl,1); /* attempt moving to line,store returned val */
long long cnt=0; // cnt -> number of chars found
if(f==0){ // if line exists,then :
while(1){
int g = fgetc(fyl);
if (g==EOF) // EOF checked in case line is last line
break;
else if(g=='\n'){ // '\n' is EOL,hence it is counted and then loop is terminated .
cnt++; break;
}
else
cnt++;
}
rewind(fyl);
return cnt;
}
else
return -1; // if line doesn't exist,return -1
}
int clone(FILE *wfrm,FILE *wto){
// clones wfrom ("Write From ") onto wto ("Write To") until EOF is encountered.
while(1){
int a =fgetc(wfrm);
if(a==EOF)
break;
else
fputc(a,wto);
}
return 0;
}
void writer(FILE *write){
// Allows basic console line-level I/O for writing to FILE *
printf("\n Terminate Input with \"/end/\".\n\n\tType below :\n\n");
char in[501]; /* str that stores input line-by-line */
char *p; int o;
while(1){
fgets(in,stdin); /* takes line from user */
if((p=strstr(in,"/end/"))!=0){
/* if line has "/end/",all chars till /end/ are written to file and input loop breaks */
o = p-in;
fprintf(write,in);
break;
}
else{
/* writes line to file */
fputs(in,write);
}
}
}
void eat() /* clears stdin */
{
int eat;while ((eat = getchar()) != '\n' && eat != EOF);
}
int main(){
/* main to add/insert to file @ given index */
char fadd[501]=""; // String to store fname
printf("\n Filename : "); scanf("%500[^\n]",fadd); eat(); // Take fname,clear stdin .
FILE * add = fopen(fadd,"r"); // open file
if(add==NULL)
perror("\n Error ");
else{
// If File is loaded for reading successfully
long long line,col; char sep; // line,col and seperating char make up the index
printf("\n Index : "); scanf("%lld%c%lld",&sep,&col); eat(); // take index,clear stdin
FILE * tmp=fopen("Temp.Ctt","w"); // open a temporary file
if(tmp==NULL)
perror("\n Error ");
else{
int f;
if(line>=1 && col>1){ // copy till the line,col-1
f = chkncpy(add,tmp,1,col-1);
}
else if(line>1 && col==1){ // copy till line-1,last char
f = chkncpy(add,line-1,lcc(add,line-1));
}
else if(line==1 && col==1){ // no moving/copying necessary at all
f=0;
}
else{
printf("\n Invalid Index.\n");f=-1;
}
if(f==0){ // if Index was not invalid
writer(tmp); // let user write to temp file
clone(add,tmp); //clones the rest of add to tmp - both are *not* fclosed
int ok = fclose(tmp); fclose(add);
if(ok==EOF){
/* if closing tmp was unsuccessful,so must be removed */
remove("Temp.Ctt");perror("\n Error ");
}
else{
if(rename("Temp.Ctt",fadd)==0)
printf("\n Success.\n");
else{
/* on Windows & some other non-POSIX systems,hence delete original */
remove(fadd);
if(rename("Temp.Ctt",fadd)==0)
printf("\n Success.\n");
else{
/* if rename still unsuccessful,throw an error,point user to temp file and give up */
perror("\n Error ");
printf("\n %s lost. File-buffer exists as %s in cwd.\n",fadd,"Temp.Ctt");
}
}
}
}
else
remove("Temp.Ctt");
}
}
return 0;
}
欢迎提出任何可能改善答案的建设性批评。如果有任何意外错误或缺少详细信息，请发表评论，我会尽快答复。