Reading a file using fgetc() but characters are skipped. Only when I use fseek() to to move the cursor one step back then it works fine. My issue is I cannot for the life of me wrap my head around it why do I need to use fseek() to solve the problem. I need fresh eyes to explain since my brain is in a lock state.

使用fgetc()读取文件，但跳过字符。只有当我使用fSeek()将光标向后移动一步时，它才能正常工作。我的问题是，我无论如何都不能理解它，为什么我需要使用fSeek()来解决这个问题。我需要新鲜的眼睛来解释，因为我的大脑处于锁定状态。

Code below skips a character

下面的代码跳过一个字符

int file_chars = 0;
size_t hdr_size = 15;
char hdr_cook_val[hdr_size];
esp_err_t get_cookie = httpd_req_get_cookie_val(req,COOKIE_NAME,hdr_cook_val,&hdr_size);
if(get_cookie == ESP_ERR_NOT_FOUND && req->uri[0] == '/' && req->method == HTTP_GET){
     FILE *index_file = fopen(HTML_PART_FOLDER"/index.txt","r");
     char *hdr_val = malloc(sizeof(char)*MALLOC_DEFAULT_SIZE);
     if(hdr_val==NULL){ESP_LOGE(TAG,"Malloc failed variable name: hdr_val");return ESP_OK;}
     for(int i=0;;i++){
         file_chars = fgetc(index_file);
         if(file_chars==EOF){
             httpd_resp_send_chunk(req,hdr_val,i);
             httpd_resp_send_chunk(req,NULL,0);
             break;
         }
         hdr_val[i] = file_chars;
         if(i==9999){
             httpd_resp_send_chunk(req,hdr_val,i);
             i=-1;
             vTaskDelay(pdMS_TO_TICKS(20));
         }
     }
     free(hdr_val);
     fclose(index_file);
     return ESP_OK;
}

using the same code but only adding the line fseek(index_file,ftell(index_file)-1,SEEK_SET); all is good

使用相同的代码，但只添加行fSeek(index_file，ftell(Index_File)-1，ek_set)；一切都很好

int file_chars = 0;
size_t hdr_size = 15;
char hdr_cook_val[hdr_size];
esp_err_t get_cookie = httpd_req_get_cookie_val(req,COOKIE_NAME,hdr_cook_val,&hdr_size);
if(get_cookie == ESP_ERR_NOT_FOUND && req->uri[0] == '/' && req->method == HTTP_GET){
     FILE *index_file = fopen(HTML_PART_FOLDER"/index.txt","r");
     char *hdr_val = malloc(sizeof(char)*MALLOC_DEFAULT_SIZE);
     if(hdr_val==NULL){ESP_LOGE(TAG,"Malloc failed variable name: hdr_val");return ESP_OK;}
     for(int i=0;;i++){
         file_chars = fgetc(index_file);
         if(file_chars==EOF){
             httpd_resp_send_chunk(req,hdr_val,i);
             httpd_resp_send_chunk(req,NULL,0);
             break;
         }
         hdr_val[i] = file_chars;
         if(i==9999){
             httpd_resp_send_chunk(req,hdr_val,i);
             fseek(index_file,ftell(index_file)-1,SEEK_SET);
             i=-1;
             vTaskDelay(pdMS_TO_TICKS(20));
         }
     }
     free(hdr_val);
     fclose(index_file);
     return ESP_OK;
}

The code loads until the 10,000th character, then only sends 9999 of them.

该代码加载到第10,000个字符，然后仅发送9999个字符。

Try this:

试试这个：

     int i = 0;
     for( ;; ) {
         file_chars = fgetc(index_file);
         if( file_chars == EOF ) {
             httpd_resp_send_chunk(req,hdr_val,i);
             httpd_resp_send_chunk(req,NULL,0);
             break;
         }
         hdr_val[ i ] = file_chars;
         // count that character and test for complete batch
         if( ++i == 10000 ) {
             httpd_resp_send_chunk( req, hdr_val, i ); // Send 10000 per batch
             i = 0;
             vTaskDelay(pdMS_TO_TICKS(20));
         }
     }

And, learn to use the spacebar... Dense code is both difficult to read and provides shelter for bugs.

还有，学会使用空格键。密集的代码既难于阅读，又为错误提供了庇护所。

EDIT:

On reflection, if the source file is an exact multiple of 10000, the code above will send two empty 'chunks'. This is not good! The following is more compact while fixing that problem. PLUS, 10000 is a magic number that should be identified somehow.

编辑：在反射时，如果源文件正好是10000的倍数，则上面的代码将发送两个空的“块”。这真是不太好!在解决该问题时，以下内容更加紧凑。此外，10000是一个神奇的数字，应该以某种方式识别出来。

#define BYTES_PER_OUT_CHUNK  10000 // why 10000? Why not...

    int i = 0;
    while( ( file_chars = fgetc( index_file ) ) != EOF ) {
        hdr_val[ i++ ] = file_chars;
        if( i == BYTES_PER_OUT_CHUNK ) {
            httpd_resp_send_chunk( req, hdr_val, i );
            i = 0;
            vTaskDelay( pdMS_TO_TICKS( 20 ) );
        }
    }
    if( i )
        httpd_resp_send_chunk( req, hdr_val, i );
    httpd_resp_send_chunk( req, NULL, 0 );