我正在尝试使用c ++读取文件，但我只想存储某些内容。这就是我的文件的样子
stufff
stuff
more stuff
.
.
.
data_I_want 32 34 45
data_I_want 52 22 34
stuff again
.
.
.
end of file
到目前为止，我已编写此代码，但输出始终为0.
ifstream file;
file.open("stuff.txt");
string line;
double v;
if(file.is_open()){
while(getline(file,line) && line.compare("data_I_want")){
file>>v;
cout<<v<<endl;
}
file.close();
}
答案 0 :(得分：0)
行是data_I_want 32 34 45，而不仅仅是data_I_want。您可能想要查找以data_I_want
开头的行以下是你如何使用字符串的get substring（取自here）：
activity | timestamp | source | source_elapsed
--------------------------------------------------------------------------------------------------+--------------+----------+----------------
execute_cql3_query | 09:00:11,930 | 10.1.1.5 | 0
Parsing select * from datachannel_6min where channel_id = 1042 order by time_start desc limit 1; | 09:00:11,930 | 10.1.1.5 | 102
Preparing statement | 09:00:11,930 | 10.1.1.5 | 233
Executing single-partition query on datachannel_6min | 09:00:11,931 | 10.1.1.5 | 1135
Acquiring sstable references | 09:00:11,931 | 10.1.1.5 | 1163
Merging memtable tombstones | 09:00:11,931 | 10.1.1.5 | 1185
Key cache hit for sstable 14912 | 09:00:11,931 | 10.1.1.5 | 1223
Seeking to partition indexed section in data file | 09:00:11,931 | 10.1.1.5 | 1230
Key cache hit for sstable 14823 | 09:00:11,984 | 10.1.1.5 | 53805
Seeking to partition indexed section in data file | 09:00:11,984 | 10.1.1.5 | 53851
Key cache hit for sstable 14786 | 09:00:12,059 | 10.1.1.5 | 129027
Seeking to partition indexed section in data file | 09:00:12,059 | 10.1.1.5 | 129060
Key cache hit for sstable 14749 | 09:00:12,241 | 10.1.1.5 | 311521
Seeking to partition indexed section in data file | 09:00:12,241 | 10.1.1.5 | 311558
Key cache hit for sstable 14714 | 09:00:12,242 | 10.1.1.5 | 311843
Seeking to partition indexed section in data file | 09:00:12,242 | 10.1.1.5 | 311849
Partition index with 0 entries found for sstable 14913 | 09:00:12,242 | 10.1.1.5 | 312153
Seeking to partition indexed section in data file | 09:00:12,242 | 10.1.1.5 | 312159
Partition index with 0 entries found for sstable 14914 | 09:00:12,354 | 10.1.1.5 | 423820
Seeking to partition indexed section in data file | 09:00:12,354 | 10.1.1.5 | 423849
Partition index with 0 entries found for sstable 14916 | 09:00:12,354 | 10.1.1.5 | 424455
Seeking to partition indexed section in data file | 09:00:12,354 | 10.1.1.5 | 424463
Partition index with 0 entries found for sstable 14915 | 09:00:12,420 | 10.1.1.5 | 490468
Seeking to partition indexed section in data file | 09:00:12,420 | 10.1.1.5 | 490501
Partition index with 0 entries found for sstable 14917 | 09:00:12,492 | 10.1.1.5 | 561711
Seeking to partition indexed section in data file | 09:00:12,492 | 10.1.1.5 | 561748
Partition index with 146 entries found for sstable 14918 | 09:00:12,696 | 10.1.1.5 | 766248
Seeking to partition indexed section in data file | 09:00:12,696 | 10.1.1.5 | 766306
Skipped 0/11 non-slice-intersecting sstables, included 0 due to tombstones | 09:00:12,696 | 10.1.1.5 | 766323
Merging data from memtables and 11 sstables | 09:00:12,696 | 10.1.1.5 | 766329
Read 2 live and 0 tombstoned cells | 09:00:12,773 | 10.1.1.5 | 842632
Request complete | 09:00:12,773 | 10.1.1.5 | 843350
activity | timestamp | source | source_elapsed
--------------------------------------------------------------------------------------------------+--------------+----------+----------------
execute_cql3_query | 09:05:46,255 | 10.1.1.4 | 0
Message received from /10.1.1.4 | 09:05:46,250 | 10.1.1.5 | 21
Executing single-partition query on datachannel_6min | 09:05:46,250 | 10.1.1.5 | 520
Acquiring sstable references | 09:05:46,250 | 10.1.1.5 | 593
Merging memtable tombstones | 09:05:46,250 | 10.1.1.5 | 609
Bloom filter allows skipping sstable 14912 | 09:05:46,250 | 10.1.1.5 | 630
Bloom filter allows skipping sstable 14823 | 09:05:46,250 | 10.1.1.5 | 641
Bloom filter allows skipping sstable 14786 | 09:05:46,250 | 10.1.1.5 | 647
Bloom filter allows skipping sstable 14749 | 09:05:46,250 | 10.1.1.5 | 654
Bloom filter allows skipping sstable 14714 | 09:05:46,251 | 10.1.1.5 | 757
Bloom filter allows skipping sstable 14913 | 09:05:46,251 | 10.1.1.5 | 763
Bloom filter allows skipping sstable 14914 | 09:05:46,251 | 10.1.1.5 | 770
Bloom filter allows skipping sstable 14916 | 09:05:46,251 | 10.1.1.5 | 776
Bloom filter allows skipping sstable 14915 | 09:05:46,251 | 10.1.1.5 | 783
Bloom filter allows skipping sstable 14917 | 09:05:46,251 | 10.1.1.5 | 789
Parsing select * from datachannel_6min where channel_id = 1036 order by time_start desc limit 1; | 09:05:46,255 | 10.1.1.4 | 103
Preparing statement | 09:05:46,255 | 10.1.1.4 | 223
Sending message to /10.1.1.5 | 09:05:46,256 | 10.1.1.4 | 673
Partition index with 17 entries found for sstable 14918 | 09:05:46,534 | 10.1.1.5 | 283815
Seeking to partition indexed section in data file | 09:05:46,534 | 10.1.1.5 | 283851
Skipped 0/11 non-slice-intersecting sstables, included 0 due to tombstones | 09:05:46,534 | 10.1.1.5 | 283867
Merging data from memtables and 1 sstables | 09:05:46,534 | 10.1.1.5 | 283873
Read 2 live and 0 tombstoned cells | 09:05:46,571 | 10.1.1.5 | 321319
Enqueuing response to /10.1.1.4 | 09:05:46,571 | 10.1.1.5 | 321439
Sending message to /10.1.1.4 | 09:05:46,571 | 10.1.1.5 | 321613
Message received from /10.1.1.5 | 09:05:46,579 | 10.1.1.4 | 323621
Processing response from /10.1.1.5 | 09:05:46,579 | 10.1.1.4 | 323730
Request complete | 09:05:46,579 | 10.1.1.4 | 324458
activity | timestamp | source | source_elapsed
--------------------------------------------------------------------------------------------------+--------------+----------+----------------
execute_cql3_query | 05:39:12,430 | 10.1.1.4 | 0
Parsing select * from datachannel_6min where channel_id = 1030 order by time_start desc limit 1; | 05:39:12,430 | 10.1.1.4 | 164
Preparing statement | 05:39:12,430 | 10.1.1.4 | 310
Sending message to /10.1.1.6 | 05:39:12,431 | 10.1.1.4 | 829
Message received from /10.1.1.4 | 05:39:12,432 | 10.1.1.6 | 19
Executing single-partition query on datachannel_6min | 05:39:12,433 | 10.1.1.6 | 719
Acquiring sstable references | 05:39:12,433 | 10.1.1.6 | 742
Merging memtable tombstones | 05:39:12,433 | 10.1.1.6 | 769
Bloom filter allows skipping sstable 1476 | 05:39:12,433 | 10.1.1.6 | 830
Partition index with 0 entries found for sstable 1475 | 05:39:12,433 | 10.1.1.6 | 904
Seeking to partition indexed section in data file | 05:39:12,433 | 10.1.1.6 | 919
Partition index with 2 entries found for sstable 1346 | 05:39:12,434 | 10.1.1.6 | 1403
Seeking to partition indexed section in data file | 05:39:12,434 | 10.1.1.6 | 1425
Partition index with 2 entries found for sstable 1472 | 05:39:12,434 | 10.1.1.6 | 1511
Seeking to partition indexed section in data file | 05:39:12,434 | 10.1.1.6 | 1522
Partition index with 0 entries found for sstable 586 | 05:39:12,434 | 10.1.1.6 | 1567
Seeking to partition indexed section in data file | 05:39:12,434 | 10.1.1.6 | 1578
Partition index with 146 entries found for sstable 5 | 05:39:12,434 | 10.1.1.6 | 2132
Seeking to partition indexed section in data file | 05:39:12,434 | 10.1.1.6 | 2152
Skipped 0/6 non-slice-intersecting sstables, included 0 due to tombstones | 05:39:12,434 | 10.1.1.6 | 2177
Merging data from memtables and 5 sstables | 05:39:12,434 | 10.1.1.6 | 2192
Read 2 live and 0 tombstoned cells | 05:39:13,106 | 10.1.1.6 | 673858
Enqueuing response to /10.1.1.4 | 05:39:13,106 | 10.1.1.6 | 674163
Sending message to /10.1.1.4 | 05:39:13,107 | 10.1.1.6 | 674329
Message received from /10.1.1.6 | 05:39:13,107 | 10.1.1.4 | 676882
Processing response from /10.1.1.6 | 05:39:13,107 | 10.1.1.4 | 677118
Request complete | 05:39:13,107 | 10.1.1.4 | 677344
activity | timestamp | source | source_elapsed
--------------------------------------------------------------------------------------------------+--------------+----------+----------------
execute_cql3_query | 05:40:41,322 | 10.1.1.4 | 0
Parsing select * from datachannel_6min where channel_id = 1028 order by time_start desc limit 1; | 05:40:41,322 | 10.1.1.4 | 104
Preparing statement | 05:40:41,322 | 10.1.1.4 | 257
Sending message to /10.1.1.5 | 05:40:41,322 | 10.1.1.4 | 569
Message received from /10.1.1.4 | 05:40:41,324 | 10.1.1.5 | 9
Executing single-partition query on datachannel_6min | 05:40:41,324 | 10.1.1.5 | 401
Acquiring sstable references | 05:40:41,324 | 10.1.1.5 | 410
Merging memtable tombstones | 05:40:41,324 | 10.1.1.5 | 427
Bloom filter allows skipping sstable 15658 | 05:40:41,324 | 10.1.1.5 | 451
Bloom filter allows skipping sstable 15666 | 05:40:41,324 | 10.1.1.5 | 476
Bloom filter allows skipping sstable 15892 | 05:40:41,324 | 10.1.1.5 | 489
Bloom filter allows skipping sstable 15749 | 05:40:41,324 | 10.1.1.5 | 503
Bloom filter allows skipping sstable 15874 | 05:40:41,324 | 10.1.1.5 | 514
Bloom filter allows skipping sstable 15682 | 05:40:41,324 | 10.1.1.5 | 523
Partition index with 14 entries found for sstable 14918 | 05:40:42,152 | 10.1.1.5 | 828365
Seeking to partition indexed section in data file | 05:40:42,152 | 10.1.1.5 | 828406
Skipped 0/7 non-slice-intersecting sstables, included 0 due to tombstones | 05:40:42,152 | 10.1.1.5 | 828422
Merging data from memtables and 1 sstables | 05:40:42,152 | 10.1.1.5 | 828427
Read 2 live and 0 tombstoned cells | 05:40:42,300 | 10.1.1.5 | 976825
Enqueuing response to /10.1.1.4 | 05:40:42,301 | 10.1.1.5 | 976984
Message received from /10.1.1.5 | 05:40:42,301 | 10.1.1.4 | 978829
Sending message to /10.1.1.4 | 05:40:42,301 | 10.1.1.5 | 977105
Processing response from /10.1.1.5 | 05:40:42,301 | 10.1.1.4 | 979018
Request complete | 05:40:42,301 | 10.1.1.4 | 979239