這個想法就像逐行比較字串并檢測重復的字串以逃避在我用名稱填充檔案并創建一個新檔案以放置所有字串而沒有重復的字串之后將主題放入另一個檔案，我使用了這個回圈，但是我不知道是對還是不對。它沒有用
FILE *Tr , *temp;
char test[50] , test1[50];
Tr = fopen("test.txt","w");
temp = fopen("temp1.txt" , "r");
while( !feof(temp) )
{
fgets(test , 50 , temp);
while( !feof(temp) ){
if ( fgets(test , 50 , temp) == fgets(test1 , 50 , temp) ){
printf("a string exist in the file");
}
else{ fprintf(Tr, "%s" , test1);
}
}
}
uj5u.com熱心網友回復：
以下行是錯誤的：
if ( fgets(test , 50 , temp) == fgets(test1 , 50 , temp) ){
使用==on 指標將比較實際的指標值，即記憶體地址。如果要比較實際的字串內容（即指標指向的內容），則必須strcmp改用。
此外，您應該只從輸入檔案中讀取，而不是從輸出檔案中讀取。
你還應該記住你讀過的所有字串。否則，您將無法確定當前行是否重復。
此外，同時具有相同回圈條件的外回圈和內回圈是沒有意義的：
while( !feof(temp) )
此外，!feof(temp)用作回圈條件通常是錯誤的。請參閱此問題以獲取更多資訊：
為什么“while (!feof (file))”總是錯的？
以下程式將記住最多 100 個字串，每個字串最多 100 個字符（包括終止空字符）。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define MAX_STRINGS 100
#define MAX_STRING_LEN 100
int main( void )
{
FILE *input, *output;
char strings[MAX_STRINGS][MAX_STRING_LEN];
int num_strings = 0;
char line[MAX_STRING_LEN];
//open input file
input = fopen( "input.txt", "r" );
if ( input == NULL )
{
fprintf( stderr, "Error opening input file!\n" );
exit( EXIT_FAILURE );
}
//open output file
output = fopen( "output.txt", "w" );
if ( output == NULL )
{
fprintf( stderr, "Error opening output file!\n" );
exit( EXIT_FAILURE );
}
//read one line of input per loop iteration
while ( fgets( line, sizeof line, input ) != NULL )
{
bool is_duplicate = false;
char *p;
//find newline character
p = strchr( line, '\n' );
//make sure that input buffer was large enough to
//read entire line, and remove newline character
//if it exists
if ( p == NULL )
{
if ( !feof( input ) )
{
fprintf( stderr, "Line was too long for input buffer!\n" );
exit( EXIT_FAILURE );
}
}
else
{
//remove newline character
*p = '\0';
}
//determine whether line is duplicate
for ( int i = 0; i < num_strings; i )
{
if ( strcmp( line, strings[i] ) == 0 )
{
is_duplicate = true;
break;
}
}
if ( !is_duplicate )
{
//remember string
strcpy( strings[num_strings ], line );
//write string to output file
fprintf( output, "%s\n", line );
}
}
//cleanup
fclose( output );
fclose( input );
}
給定輸入
String1
String2
String3
String4
String5
String1
String6
String2
String1
String7
String8
String1
String2
該程式具有以下輸出：
String1
String2
String3
String4
String5
String6
String7
String8
如您所見，所有重復的字串都被正確地從輸出中過濾掉了。
但是，使用靜態大小的陣列有點浪費空間，而且還施加了硬限制。因此，使用動態記憶體分配可能會更好：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define INITIAL_CAPACITY 100
#define MAX_LINE_LEN 200
int main( void )
{
FILE *input, *output;
char **strings;
size_t strings_capacity;
int num_strings = 0;
char line[MAX_LINE_LEN];
//open input file
input = fopen( "input.txt", "r" );
if ( input == NULL )
{
fprintf( stderr, "Error opening input file!\n" );
exit( EXIT_FAILURE );
}
//open output file
output = fopen( "output.txt", "w" );
if ( output == NULL )
{
fprintf( stderr, "Error opening output file!\n" );
exit( EXIT_FAILURE );
}
//set capacity of "strings" array to INITIAL_CAPACITY
strings_capacity = INITIAL_CAPACITY;
strings = malloc( strings_capacity * sizeof *strings );
if ( strings == NULL )
{
fprintf( stderr, "Memory allocation failure!\n" );
exit( EXIT_FAILURE );
}
//read one line of input per loop iteration
while ( fgets( line, sizeof line, input ) != NULL )
{
bool is_duplicate = false;
char *p;
//find newline character
p = strchr( line, '\n' );
//make sure that input buffer was large enough to
//read entire line, and remove newline character
//if it exists
if ( p == NULL )
{
if ( !feof( input ) )
{
fprintf( stderr, "Line was too long for input buffer!\n" );
exit( EXIT_FAILURE );
}
}
else
{
//remove newline character
*p = '\0';
}
//determine whether line is duplicate
for ( int i = 0; i < num_strings; i )
{
if ( strcmp( line, strings[i] ) == 0 )
{
is_duplicate = true;
break;
}
}
if ( !is_duplicate )
{
//expand capacity of "strings" array if necessary
if ( num_strings == strings_capacity )
{
strings_capacity *= 2;
strings = realloc( strings, strings_capacity * sizeof *strings );
if ( strings == NULL )
{
fprintf( stderr, "Memory allocation failure!\n" );
exit( EXIT_FAILURE );
}
}
//remember string
strings[num_strings] = malloc( strlen( line ) 1 );
if ( strings[num_strings] == NULL )
{
fprintf( stderr, "Memory allocation failure!\n" );
exit( EXIT_FAILURE );
}
strcpy( strings[num_strings], line );
num_strings ;
//write string to output file
fprintf( output, "%s\n", line );
}
}
//cleanup
//free all dynamically allocated memory
for ( int i = 0; i < num_strings; i )
free( strings[i] );
free( strings );
//close file handles
fclose( output );
fclose( input );
}
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標籤：C
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