"你好TensorFlow!" 使用C API

Question

出于学习目的,如何使用TensorFlow C API对此Python示例进行编码？

import tensorflow as tf
hello = tf.constant("hello TensorFlow!")
sess=tf.Session()
print(sess.run(hello))

我这样试过:

#include <string.h>
#include <iostream.h>
#include "c_api.h"

int main( int argc, char ** argv ) 
{
  TF_Graph * graph = TF_NewGraph();
  TF_SessionOptions * options = TF_NewSessionOptions();
  TF_Status * status = TF_NewStatus();
  TF_Session * session = TF_NewSession( graph, options, status );
  char hello[] = "Hello TensorFlow!";
  TF_Tensor * tensor = TF_AllocateTensor( TF_STRING, 0, 0, 8 + TF_StringEncodedSize( strlen( hello ) ) );
  TF_OperationDescription * operationDescription = TF_NewOperation( graph, "Const", "hello" );
  TF_Operation * operation; 
  struct TF_Output * output;

  TF_StringEncode( hello, strlen( hello ), 8 + ( char * ) TF_TensorData( tensor ), TF_StringEncodedSize( strlen( hello ) ), status );
  TF_SetAttrTensor( operationDescription, "value", tensor, status );
  TF_SetAttrType( operationDescription, "dtype", TF_TensorType( tensor ) );
  operation = TF_FinishOperation( operationDescription, status );

  output->oper = operation;
  output->index = 0;

  TF_SessionRun( session, 0,
                 0, 0, 0,  // Inputs
                 output, &tensor, 1,  // Outputs
                 &operation, 1,  // Operations
                 0, status );

  printf( "%i", TF_GetCode( status ) );

  TF_CloseSession( session, status );
  TF_DeleteSession( session, status );
  TF_DeleteStatus( status );
  TF_DeleteSessionOptions( options );  

  return 0;
}

我在Windows上使用以下命令对其进行测试TensorFlow.dll:http: //ci.tensorflow.org/view/Nightly/job/nightly-libtensorflow-windows/lastSuccessfulBuild/artifact/lib_package/libtensorflow-cpu-windows-x86_64.zip

以上代码GPF在TF_SessionRun()通话中.一旦我们找到了解决方案,如何检索输出？是否应该使用不同的张量进行输出？上面的代码在输出和操作中重用它.

非常感谢

Answer 1

偏移初始化旁边有一个要解决的错误.这个版本似乎工作正常:

#include <iostream.h>
#include "c_api.h"

int main( int argc, char ** argv ) 
{
  TF_Graph * graph = TF_NewGraph();
  TF_SessionOptions * options = TF_NewSessionOptions();
  TF_Status * status = TF_NewStatus();
  TF_Session * session = TF_NewSession( graph, options, status );
  char hello[] = "Hello TensorFlow!";
  TF_Tensor * tensor = TF_AllocateTensor( TF_STRING, 0, 0, 8 + TF_StringEncodedSize( strlen( hello ) ) );
  TF_Tensor * tensorOutput;
  TF_OperationDescription * operationDescription = TF_NewOperation( graph, "Const", "hello" );
  TF_Operation * operation; 
  struct TF_Output output;

  TF_StringEncode( hello, strlen( hello ), 8 + ( char * ) TF_TensorData( tensor ), TF_StringEncodedSize( strlen( hello ) ), status );
  memset( TF_TensorData( tensor ), 0, 8 );
  TF_SetAttrTensor( operationDescription, "value", tensor, status );
  TF_SetAttrType( operationDescription, "dtype", TF_TensorType( tensor ) );
  operation = TF_FinishOperation( operationDescription, status );

  output.oper = operation;
  output.index = 0;

  TF_SessionRun( session, 0,
                 0, 0, 0,  // Inputs
                 &output, &tensorOutput, 1,  // Outputs
                 &operation, 1,  // Operations
                 0, status );

  printf( "status code: %i\n", TF_GetCode( status ) );
  printf( "%s\n", ( ( char * ) TF_TensorData( tensorOutput ) ) + 9 );

  TF_CloseSession( session, status );
  TF_DeleteSession( session, status );
  TF_DeleteStatus( status );
  TF_DeleteSessionOptions( options );  

  return 0;
}

我们必须删除tensorOutput吗？不知道为什么我们必须添加9(而不是8)来获得字符串的开头.

Answer 2

TF_STRING张量使用此处描述的格式进行编码。在您的代码中，您占用了空间（8 个字节）来编码一个偏移量，但实际上并未对其进行初始化。为此，您需要添加类似以下内容：

memset(TF_TensorData(张量), 0, 8);

在调用之前TF_SetAttrTensor，因为这会将字符串元素的“偏移量”设置为 0（这是您对一个字符串值进行编码的位置）。

对于你的第二个问题：你实际上并没有重复使用相同的tensor指针。注释表明TF_SessionRun正在分配调用者拥有所有权的TF_SessionRun新对象。TF_Tensor因此，在您的代码片段中，tensor变量被覆盖以指向新分配的张量。

希望有帮助。