Question

我有一个字符串，我需要抓住每个字符并进行一些检查。

std::string key = "test"
int i = 0;
while (key.at(i))
{
    // do some checking
    i++;
}

问题是，最终索引i将超出范围，因此系统将崩溃。我该如何解决这个问题？

谢谢！

Answer 1

std::string key = "test"
for(int i = 0; i < key.length(); i++)
{
    //do some checking
}

Answer 2

for(auto i = key.cbegin(); i != key.cend(); ++i)
{
    // do some checking
    // call *i to get a char
}

Answer 3

另一种解决方案是使用# In[30]: import pandas as pd import h2o from h2o.estimators.gbm import H2OGradientBoostingEstimator h2o.init() # Import a sample binary outcome train/test set into H2O train = h2o.import_file("https://s3.amazonaws.com/erin-data/higgs/higgs_train_10k.csv") test = h2o.import_file("https://s3.amazonaws.com/erin-data/higgs/higgs_test_5k.csv") # Identify predictors and response x = train.columns y = "response" x.remove(y) # For binary classification, response should be a factor train[y] = train[y].asfactor() test[y] = test[y].asfactor() # Train and cross-validate a GBM model = H2OGradientBoostingEstimator(distribution="bernoulli", seed=1) model.train(x=x, y=y, training_frame=train) # In[31]: # Test AUC model.model_performance(test).auc() # 0.7817203808052897 # In[32]: # Generate predictions on a test set pred = model.predict(test) # In[33]: from sklearn.metrics import roc_auc_score, confusion_matrix pred_df = pred.as_data_frame() y_true = test[y].as_data_frame() roc_auc_score(y_true, pred_df['p1'].tolist()) #pred_df.head() # In[36]: y_true = test[y].as_data_frame().values cm = pd.DataFrame(confusion_matrix(y_true, pred_df['predict'].values)) # In[37]: print(cm) 0 1 0 1354 961 1 540 2145 # In[38]: model.model_performance(test).confusion_matrix() Confusion Matrix (Act/Pred) for max f1 @ threshold = 0.353664307031828: 0 1 Error Rate 0 964.0 1351.0 0.5836 (1351.0/2315.0) 1 274.0 2411.0 0.102 (274.0/2685.0) Total 1238.0 3762.0 0.325 (1625.0/5000.0) # In[39]: h2o.cluster().shutdown()并提供可处理每个字符的lambda函数，如下所示：

std::for_each()

此打印：

std::string key = "testing 123";
std::for_each(key.cbegin(), key.cend(), [](char c){ std::cout << c; });

Answer 4

您可以使用这样的for循环。

#include <string>

std::string str("hello");

        for(auto &c : str) {
            std::cout << c << std::endl;
        }

C ++：如何迭代字符串中的每个字符？

4 个答案: