fgets读取文件时的注意事项

1 文本文件 a.txt 内容如下

fgets读取文件时的注意事项


2 c代码
  FILE *fil;
if (!(fil = fopen("/home/rudy/projects/paser/a.txt", "rb"))) {
printf("File I/O error,the File is not exist\n");
exit(0);
}
int line = 0; while(!feof(fil)) {
if (fgetc(fil) == '\n') {
++line;
}
}
++line; fclose(fil);
if (!(fil = fopen("/home/rudy/projects/paser/a.txt", "rb"))) {
printf("File I/O error,the File is not exist\n");
exit(0);
}
char ** all =(char **) malloc( line * sizeof(char *)); for (int iCurrLineIndex = 0; iCurrLineIndex < line; ++iCurrLineIndex) { all[iCurrLineIndex] = (char *) malloc(20 ); fgets(all[iCurrLineIndex], 21, fil);
} for (int iCurrLineIndex = 0; iCurrLineIndex < line; ++iCurrLineIndex) {
printf("this is len = %d \n",strlen(all[iCurrLineIndex]));
for(int i = 0;i <11;i++) {
if (all[iCurrLineIndex][i] == '\0')
{
printf("%s\n ","this is 0");
}else if ( all[iCurrLineIndex][i]== '\n')
{
printf("%s\n ","this is n");
}else{
printf("%c ",all[iCurrLineIndex][i]);
}
}
printf("\n"); }

输出结果

 

this is len = 10
1 2 3 4 5 6 7 8 9 this is n
this is 0 this is len = 10
a b c d e f g h i this is n
this is 0 this is len = 9
1 2 3 4 5 6 7 8 9 this is 0
this is 0

总结: fgets读取时,如果指定的读取大小,小于实际行大小 那么 不添加\n做结尾,使用\0 ,然后接着读取没读完的当前行数据作为新的一行开始

    fgets读取时,如果指定读取大小.大于实际行大小,那么将\n添加到末端.再添加\0

   \0不算做有效长度里的元素,\n算有效长度里元素

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